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THE  CHEMISTRY 


OF 


SOILS  AND  FERTILIZERS 


BY 


HARRY  SNYDER,  B.S., 

Professor  of  Agricultural  Chemistry.  University  of  Minnesota. 

and  Chemist  of  the  Minnesota  Agricultural 

Experiment  Station. 


EASTON,  FA.: 
THE  CHEMICAL  FUBLISHIXG  COMPANY. 

1899. 

{All  rights  reserved.') 


.^ 


Copyright,  i?99,  by  Edward  Hart. 


PREFACE 

For  several  years  courses  of  instruction  have  been 
given  at  the  University  of  Minnesota  to  classes  of 
young  men  who  intend  to  become  farmers  and  who 
desire  information  that  will  be  of  assistance  to  them 
in  their  profession.  In  giving  this  instruction  mimeo- 
graphed notes  have  been  prepared,  but  the  increase  in 
the  number  of  students  and  the  volume  of  notes  have 
necessitated  the  publication  of  this  work.  In  its  prep- 
aration, it  has  been  the  ahh  tdJ^^ive,  in  condensed  form, 
the  principles  of  chemistry  which  have  a  bearing  upon 
the  conservation  of  soil  fertility  and  the  economic  use 

of   manures. 

Harry  Snyder. 
University  of  Minnesota, 

Coi,I,EGE  OF  AGRICUI.TURE, 

St.  Anthony  Park,  Minn. 
April  i^,  i8gg. 


^CAUFOg 

CONTENTS 


INTRODUCTION 

Early  uses  of  manures  and  the  explanation  of  their  action  by  the 
alchemists  ;  Investigations  prior  to  1800 ;  Work  of  De  Saussure, 
Davy,  Thaer,  and  Boussingault ;  Liebig's  writings  and  their  influ- 
ence ;  Investigations  of  Lawes  and  Gilbert  ;  Contributions  of 
other  investigators  ;  Agronomy.     Pages  1-9. 

CHAPTER  I 

Physical  Properties  of  Soils.  —  Chemical  and  physical  properties 
of  soils  considered ;  Weight  of  soils ;  Size  of  soil  particles ;  Clay  ; 
Sand  ;  Silt ;  Form  of  soil  particles  ;  Number  and  arrangement  of 
soil  particles  ;  Mechanical  analysis  of  soils.  Soil  types  — 
Potato  and  truck  soils ;  Fruit  soils ;  Corn  soils  ;  Medium  grass  and 
grain  soils;  Wheat  soils.  Relation  of  the  soil  to  water  ;  Amount  of 
water  required  for  crops  ;  Bottom  water  ;  Capillary  water  ;  Hydro- 
scopic water;  Loss  of  water  by  percolation,  evaporation,  and 
transpiration  ;  Influence  of  cultivation  upon  the  water  supply  of 
crops  ;  Capillary  water  and  cultivation  ;  Shallow  surface  cultiva- 
tion ;  Cultivation  after  rains  ;  Rolling ;  Sub-soiling  ;  Fall  plowing  ; 
Spring  plo\nng ;  Mulching ;  Depth  of  plowing ;  Fertilizers  and 
their  influence  upon  moisture  content  of  soils  ;  Farm  manures  and 
soil  moisture  ;  Permeability  of  soils  ;  Drainage  ;  Relation  of  soils  to 
heat ;  Heat  from  chemical  reactions  within  the  soil ;  Heat  and  crop 
growth  ;  Color  of  soils  ;  Odor  and  taste  of  soils  ;  Relation  of 
soils  to  electricity  ;  Importance  of  physical  properties  of  the  soil. 
Pages  9-48. 

CHAPTER  II 

Geological  Formation  and  Classification  of  Soils.  —  Geological 
study  of  soils  ;  Formation  of  soils  ;  Action  of  heat  and  cold ; 
Action  of   water ;  Glacial  action  ;  Chemical   action  of  water ;  Ac- 


Vi  CONTENTS 

tion  of  air  and  gases ;  Action  of  vegetation  and  micro-organisms  ; 
Distribution  of  soils ;  Sedentary  and  transported  soils  ;  Rocks 
and  minerals  from  which  soils  are  derived  as  quartz,  feldspar,  mica, 
hornblende,  zeolites,  granite,  apatite,  kaolin,  limestone,  gypsum  ; 
Chemical  composition  of  rocks.     Pages  49-59. 

CHAPTER  III 

Chemical  Composition  of  Soils.  —  Elements  combine  to  form 
minerals  ;  Classification  of  elements ;  Combination  of  elements  ; 
Forms  in  which  elements  are  present  in  soils  ;  Acid-forming  ele- 
ments, silicon,  double  silicates,  carbon,  sulphur,  chlorine,  phos- 
phorus, nitrogen,  oxygen,  hydrogen  ;  Base-forming  elements,  alu- 
minum, potassium,  calcium,  magnesium,  sodium,  iron  ;  Classifica- 
tion of  elements  for  plant-food  purposes;  Amount  of  plant  food  in 
different  forms  in  various  types  of  soils ;  How  a  soil  analysis  is 
made  ;  Value  of  soil  analysis ;  Interpretation  of  the  results  of  soil 
analvsis  ;  Use  of  dilute  acids  as  solvents  in  soil  anah'sis;  Distribu- 
tion of  plant  food  in  the  soil ;  Composition  of  typical  soils ; 
"Alkali"  soils  and  their  improvement;  Organic  compounds 
of  soil ;  Sources  ;  Classification  ;  Humus  ;  Humates  ;  Humification  ; 
Humates  produced  by  different  kinds  of  organic  matter ;  Value 
of  humates  as  plant  food,  amount  of  plant  food  in  humic  forms  ; 
IvOss  of  humus  by  forest  fires,  by  prairie  fires,  by  cultivation  ; 
Humic  acid  ;  Soils  in  need  of  humus  ;  Soils  not  in  need  of  humus ; 
Composition  of  humus  from  old  and  new  soils  ;  Influence  of  different 
methods  of  farming  upon  humus.     Pages  60-101. 

CHAPTER  IV 

Nitrogen  of  the  Soil  and  Air,  Nitrification  and  Nitrogenous  Ma- 
nures. —  Importance  of  nitrogen  as  plant  food  ;  Atmospheric 
nitrogen  as  a  source  of  plant  food.  Experiments  of  Boussingault, 
Ville,  and  Lawes  and  Gilbert  ;  Result  of  field  trials  ;  Experiments 
of  Hellriegel  and  Wilfarth  and  recent  investigators  ;  Composition 
of  root  nodules  ;  Amount  of  nitrogen  returned  to  soil  by  leguminous 
crops  and  importance  to  agriculture  ;  Nitrogenous  compounds 
of  the  soil  ;  Origin  ;  Organic  nitrogen  ;  Amount  of  nitrogen  in  soils  ; 
Rem  jved  in  crops  ;  Nitrates  and  nitrites  ;  Anunonium  compounds  ; 


CONTENTS  vii 

Ammonia  in  rain  and  drain  waters  ;  Ratio  of  nitrogen  to  carbon  in 
the  soil ;  Losses  of  nitrogen  from  soils  ;  Gains  of  nitrogen  to  soils ; 
Nitrification  ;  Former  views  regarding  ;  Workings  of  an  organism  ; 
Conditions  necessary  for  nitrification  ;  Influence  of  cultivation 
upon  these  conditions  ;  Nitrous  acid  organisms,  ammonia-produ- 
cing organisms,  denitrification,  number  and  kind  of  organisms  in 
soils  ;  Inoculation  of  soils  with  organisms  ;  Chemical  products  pro- 
duced by  organisms ;  Losses  of  nitrogen  by  fallowing  rich  prairie 
lands  ;  Deep  and  shallow  plowing  and  nitrification  ;  Spring  and 
fall  plowing  and  nitrification  ;  Nitrogenous  manures  ;  Sources  ; 
Dried  blood,  tankage,  flesh  meal,  fish  scrap,  seed  residue,  and  uses 
of  each  ;  Leather,  wool  waste,  and  hair  ;  Peat  and  muck  ;  Legumi- 
nous crops  as  nitrogenous  fertilizers  ;  Sodium  nitrate,  ammonium 
salts  ;  Cost  and  value  of  nitrogenous  fertilizers.     Pages    102-137. 

CHAPTER  V 

Fixation.  —  Fixation  a  chemical  change,  examples  of  ;  Due  to 
zeolites  ;  Humus  and  fixation  ;  Other  compounds  of  soil  cause  fixa- 
tion ;  Soils  possess  dififerent  powers  of  fixation  ;  Nitrates  do  not 
undergo  fixation  ;  Fixation  of  phosphates  ;  Fixation  a  desirable 
property  of  soils  ;  Fixation  and  the  action  of  manures.  Pages  138- 
140. 

CHAPTER  VI 

Farm  Manures.  —  Variable  composition  of  farm  manures  ;  Factors 
which  influence  composition  of  manures  ;  Absorbents  ;  Relation  of 
food  consumed  to  manures  produced  ;  Bulky  and  concentrated 
foods  ;  Course  of  the  nitrogen  of  the  food  during  digestion  ;  Com- 
position of  liquid  and  solid  excrements  ;  Manurial  value  of  foods  ; 
Commercial  valuation  of  manure  ;  Influence  of  age  and  kind  of 
animal  ;  Manure  from  young  and  old  animals ;  Cow  manure ; 
Horse  manure  ;  Sheep  manure  ;  Hog  manure  ;  Hen  manure  ;  Mix- 
ing manures  ;  Volatile  products  from  manure  ;  Human  excrements  • 
Preservation  of  manures  ;  Leaching  ;  Losses  by  fermentation  ; 
Different  kinds  of  fermentation  ;  Water  necessary  for  fermenta- 
tion ;  Composting  manures  ;  Uses  of  preservatives  ;  Manure  pro- 
duced in  sheds  ;  UvSe  of  manures  ;  Direct  hauling  to  field ; 
Coarse  manures  may  be  injurious ;  Manuring  pasture  land  ;  Small 


VIU  CONTENTS 

piles  of  manure  in  fields  objectionable  ;  Rate  of  application  ;  Most 
suitable  crops  to  apply  to  ;  Comparative  value  of  manure  and  food  ; 
Comparative  value  of  good  and  poor  manure  ;  Summary  of  ways  in 
which  manures  may  be  beneficial.     Pages  141-171. 

CHAPTER  VII 

Phosphate  Fertilizers.  —  Importance  of  phosphorus  as  plant  food  ; 
Amount  of  phosphoric  acid  in  soils,  amount  removed  in  crops ; 
Source  of  soil  phosphoric  acid  ;  Commercial  forms  of  phosphoric 
acid  ;  Phosphate  rock  ;  Calcium  phosphates  ;  Reverted  phosphoric 
acid  ;  Available  phosphoric  acid  ;  Manufacture  of  phosphate  fertil- 
izers, acid  phosphates,  superphosphates ;  Commercial  value  of 
phosphoric  acid  ;  Basic  slag  phosphates  ;  Guano  ;  Bones  ;  Steamed 
bone  ;  Dissolved  bone  ;  Bone  black  ;  Use  of  phosphate  fertilizers  ; 
How  to  keep  the  phosphoric  acid  of  the  soil  available.  Pages  172- 
185.  ^^ 

CHAPTER  VIII 

Potash  Fertilizers.  —  Potassium  an  essential  element ;  Amount  of 
potash  removed  in  crops  ;  Amount  in  soils  ;  Source  of  soil  potash ; 
Commercial  forms  of  potash  ;  Stassfurt  salts,  occurrence  of ; 
Kainit ;  Sulphate  of  potash  ;  Other  Stassfurt  salts  ;  Wood  ashes, 
composition  of ;  Amount  of  ash  in  different  kinds  of  wood  ;  Action 
of  ashes  on  soils  ;  Leached  ashes  ;  The  alkalinity  of  ashes  ;  Coal 
ashes  ;  Miscellaneous  ashes  ;  Commercial  value  of  potash  ;  Use  of 
potash  fertilizers;  Joint  use  of  potash  and  lime.     Pages  186-195. 

CHAPTER  IX 

Lime  and  Miscellaneous  Fertilizers.  —  Calcium  an  essential  ele- 
ment ;  Amount  of  lime  removed  in  crops  ;  Amount  of  lime  in  soils ; 
Different  kinds  of  lime  fertilizers  ;  Their  physical  and  chemical 
action  ;  Action  of  lime  upon  organic  matter  and  correcting  acidity 
of  soils  ;  Ivime  liberates  potash  ;  Aids  nitrification  ;  Action  of  land 
plaster  on  some  "alkali"  soils;  Quicklime  and  slaked  lime  ; 
Marl  ;  Physical  action  of  lime  ;  Judicious  use  of  lime  ;  Miscel- 
laneous fertilizers  ;  Salt  and  its  action  on  the  soil  ;  Magnesium 
salts  ;  Soot ;  Sea-weed  ;  Strand  plants  ;  Wool  washings.  Pages 
196-204. 


CONTENTS  IX 

CHAPTER  X. 

Commercial  Fertilizers.  —  History  of  development  of  industry  ; 
Complete  fertilizers  and  amendments  ;  Variable  composition  of 
commercial  fertilizers  ;  Preparation  of  fertilizers  ;  Inert  forms 
of  matter  in  fertilizers ;  Inspection  of  fertilizers;  Mechanical 
condition  of  fertilizers  ;  Forms  of  nitrogen,  phosphoric  acid, 
and  potash  in  commercial  fertilizers  ;  Misleading  statements  on 
fertilizer  bags  ;  Estimating  the  value  of  a  fertilizer  ;  Home  mixing  ; 
Fertilizers  and  tillage  ;  Abuse  of  commercial  fertilizers  ;  Proper 
use  of  ;  Field  tests  ;  General  principles  ;  Preliminary  experiments  ; 
Verifying  results  ;  Deficiency  of  one  element  ;  Deficienc}-  of  two 
elements;  Will  it  pay  to  use  fertilizers?  Amount  to  use  per  acre  ; 
Influence  of  excessive  applications  ;  Fertilizing  special  crops  ;  Com- 
mercial fertilizers  and  farm  manures.     Pages  205-224. 

CHAPTER  XI. 

Food  Requirements  of  Crops. — Amount  of  fertility  removed  by 
crops  ;  Assimilative  powers  of  crops  compared  ;  Way  in  which 
plants  obtain  their  food  ;  Cereal  crops  ;  General  food  requirements ; 
Wheat ;  Barley  ;  Oats  ;  Corn  ;  Miscellaneous  crops ;  Flax  ;  Pota- 
toes ;  Sugar-beets  ;  Roots  ;  Turnips  ;  Rape  ;  Buckwheat ;  Cotton  ; 
Hops  ;  Hay  and  grass  crops  ;  Leguminous  crops.     Pages  225-237. 

CHAPTER  XII. 

Rotation  of  Crops.  — Object  of  rotating  crops  ;  Principles  involved 
in  crop  rotation  ;  Deep  and  shallow  rooted  crops ;  Humus-consu- 
ming and  humus-producing  crops  ;  Crop  residues  ;  Nitrogen-consu- 
ming and  nitrogen-producing  crops ;  Rotation  and  mechanical 
condition  of  soil  ;  Economic  use  of  soil  water ;  Rotation  and  farm 
labor  ;  Economic  use  of  manures  ;  Salable  crops  ;  Rotations  advan- 
tageous in  other  ways ;  Long-  and  short-course  rotations  ;  Problems 
in  rotations  ;  Conserv^ation  of  fertility  ;  Necessity  of  manures  ; 
Uses  of  crops  ;  Losses  of  fertility  with  difi^erent  methods  of  farming  ; 
Problems  on  income  and  outgo  of  fertility  from  farm.  Pages  238- 
254. 

References  ;  Experiments  ;  Review  Questions  ;  Corrections. 
Pages  255-272. 


THE  CHEMISTRY  OF 

SOILS  AND  FERTILIZERS 


INTRODUCTION 

Prior  to  1800  but  little  was  known  of  the  sources 
and  importance  of  plant  food.  Manures  had  been 
used  from  the  earliest  times,  and  their  value  w^as  rec- 
ognized, but  the  fundamental  principles  underlying 
their  use  were  not  understood.  It  was  believed  that 
they  acted  in  some  mysterious  way.  The  alchemists 
had  advanced  various  views  regarding  theii  action  ; 
one  was  that  the  so-called  "spirits"  left  the  decaying 
manure  and  entered  the  plant,  producing  more  vigor- 
ous growth.  As  evidence,  the  worthless  character  of 
leached  manure  was  cited.  It  was  believed  that  the 
spirits  had  left  such  manure.  The  terms  'spirits  of 
hartshorn',  'spirits  of  niter',  'spirits  of  turpentine',  and 
many  others  reflect  these  ideas  regarding  the  compo- 
sition of  matter. 

Before  the  composition  of  plant  and  animal  bodies 
was  established,  it  was  believed  that  one  substance, 
like  copper,  could  be  changed  to  another  substance,  as 
gold.     Plants  were  supposed  to  be  water  transmuted 


2.  SOILS    AND    FERTILIZERS 

in  some  mysterious  way  directly  into  plant  tissue.  Van 
Helmont,  in  the  seventeenth  century,  attempted  to 
prove  this.  "  He  took  a  large  earthen  vessel  and  filled 
it  with  200  pounds  of  dried  earth.  In  it  he  planted  a 
willow  weighing  five  pounds,  which  he  duly  watered 
with  rain  and  distilled  water.  After  five  years  he 
pulled  up  the  willow  and  it  now  weighed  one  hundred 
and  sixty-nine  pounds  and  three  ounces."'  He  con- 
cluded that  164  pounds  of  roots,  bark,  leaves,  and 
branches  had  been  produced  by  the  direct  transmuta- 
tion of  the  water. 

It  is  evident  from  the  preceding  example  that  au}- 
thing  like  an  adequate  idea  of  the  growth  and  compo- 
sition of  plant  bodies  could  not  be  gained  until  the 
composition  of  air  and  water  were  established. 

The  discovery  of  oxygen  by  Priestley  in  1774, 
of  the  composition  of  water  by  Cavendish  in 
1 781,  and  of  the  role  which  carbon  dioxide  plays  in 
plant  and  animal  life  by  DeSaussure  and  others  in 
1800,  form  the  nucleus  of  our  present  knowledge  re- 
garding the  sources  of  matter  stored  up  in  plants.  It 
was  from  1760  to  1800  that  alchemy  lost  its  grip  and 
the  way  was  prepared  for  the  development  of  modern 
chemistry. 

The  work  of  DeSaussure,  entitled  ^'Recherches 
sur  la  Vegetation,''  published  in  1804,  was  the  first 
svstematic  work  showino^  the  sources  of  the  com- 
pounds  stored  up  in  plant  bodies.      He  demonstrated, 


INTRODUCTION  3 

quantitatively,  that  the  increase  in  the  amount  of 
carbon,  hydrogen,  and  oxygen,  when  plants  were  ex- 
posed to  sunlight,  was  at  the  expense  of  the  carbon 
dioxide  of  the  air,  and  of  the  water  of  the  soil.  He 
also  maintained  that  the  mineral  elements  derived 
from  the  soil  were  essential  for  plant  growth,  and  gave 
the  results  of  the  analyses  of  many  plant  ashes.  He 
believed  that  the  nitrogen  of  the  soil  w^as  the  main 
source  of  the  nitrogen  found  in  plants.  These  views 
have  since  been  verified  by  many  investigators,  and 
are  substantially  those  held  at  the  present  time  re- 
garding the  fundamental  principles  of  plant  growth. 
They  were  not,  however,  accepted  as  conclusive  at 
the  time,  and  it  was  not  until  nearly  a  half  century 
later,  when  Boussingault,  Liebig,  and  others  repeated 
the  investigations  of  DeSaussure,  that  they  were 
finally  accepted  by  chemists  and  botanists. 

From  the  time  of  DeSaussure  to  1835,  scientific 
experiments  relating  to  plant  growth  were  not  actively 
prosecuted,  but  the  scientific  facts  which  had  accumu- 
lated were  studied  and  attempts  were  made  to  apply 
the  results  to  actual  practice.  Among  the  first  to  see 
the  relation  between  chemistry  and  agriculture  was 
Sir  Humphry  Davy.  In  181 3  he  published  his 
"  Essentials  of  Agricultural  Chemistry",  which  treated 
of  the  composition  of  air,  soil,  manures,  plants,  and 
of  the  influence  of  light  and  heat  upon  plant  growth. 
About  this  same  period,  Thaer  published  an  important 


4  SOILS   AND    FERTILIZERS 

work  entitled  ^'  Principes  Raisonnes  d'  Agriculture". 
Thaer  believed  that  humus  determined  the  fertility  of 
the  soil,  that  plants  obtained  their  food  mainly  from 
humus,  and  that  the  carbon  compounds  of  plants 
were  produced  from  the  organic  carbon  compounds  of 
the  soil.  This  gave  rise  to  the  so-called  humus  theory, 
wdiich  was  later  shown  to  be  an  inaccurate  idea  re- 
garding the  source  of  plant  food.  The  writings  of 
Thaer  were  of  a  most  practical  nature,  and  they  did 
much  to  stimulate  later  investigations. 

About  1830  there  was  a  renewed  interest  in  scientific 
investigations  relating  to  agriculture.  At  this  time 
Boussino;-ault  became  activelv  eng^aofed  in  ao^ricul- 
tural  research.  He  was  the  first  to  establish  a  chemical 
laboratory  upon  a  farm  and  to  make  practical  inves- 
tigations in  connection  with  agriculture.  This  marks 
the  establishment  of  the  first  agricultural  experi- 
ment station.  Boussingault's  work  upon  the  as- 
similation of  the  free  nitrogen  of  the  air  is  reviewed 
in  Chapter  IV.  His  study  of  the  rotation  of  crops 
was  a  valuable  contribution  to  agricultural  science. 
He  discovered  many  important  facts  relating  to  the 
chemical  characteristics  of  foods,  and  was  the  first  to 
make  a  comparative  study  of  the  amount  of  nitrogen 
in  different  kinds,  of  foods  and  to  determine  the  value 
of  foods  on  the  basis  of  the  nitrogen  content.  His 
study  of  the  production  of  saltpeter  did  much  to  pre- 
pare the   way  for  later  work   on   nitrification.     The 


INTRODUCTION  5 

work  of  Boussiiigault  covered  a  \-ariety  of  subjects  re- 
lating to  plant  growth.  He  repeated  and  verified 
much  of  the  earlier  work  of  DeSaussure,  and  also 
secured  man}'  additional  facts  relating  to  the  chemis- 
try of  crop  growth.  As  to  the  source  of  nitrogen  in 
crops,  he  states  that :  "The  soil  furnishes  the  crops 
with  mineral  alkaline  substances,  provides  them  with 
nitrogen,  by  ammonia  and  by  nitrates,  which  are 
formed  in  the  soil  at  the  expense  of  the  nitrogenous 
matters  contained  in  diluvium,  which  is  the  basis  of 
vegetable  earth  ;  compounds  in  wdiich  nitrogen  exists 
in  stable  combination,  onh-  becoming  fertilizing  by 
the  effect  of  time."  As  for  the  absorption  of  the  gas- 
eous nitrogen  of  the  air  b}'  vegetable  earth,  he  sa}'s  : 
"  I  am  not  acquainted  with  a  single  irreproachable  ob- 
servation that  establishes  it ;  not  onh'  does  the  earth 
not  absorb  gaseous  nitrogen,  but  it  gives  it  off."" 

The  investigations  of  DeSaussure  and  Boussingault, 
and  the  writings  of  Da\'y,  Thaer,  Sprengel,  and  Schiib- 
ler  prepared  the  wa}'  for  the  work  and  writings  of 
Iviebig.  In  1840  he  published  "Organic  Chemistry 
in  its  Applications  to  Agriculture  and  PliA'siology". 
Liebig's  agricultural  investigations  were  preceded  by 
many  valuable  discoveries  in  organic  chemistry,  which 
he  applied  directly  in  his  interpretations  of  ao-ricul- 
tural  problems.  His  writings  were  of  a  forcible  char- 
acter and  were  extremely  argumentative.  They  pro- 
voked,   as    he    intended,    A'igorous    discussions    upon 


6  SOILS   AND    FERTILIZERS 

agricultural  problems.  He  assailed  the  humus  theory 
of  Thaer,  and  showed  that  humus  was  not  an  adequate 
source  of  the  plant's  carbon.  In  the  first  edition  of 
his  work  he  showed  that  farms  from  which  certain 
products  were  sold  naturally  became  less  productive, 
because  of  the  loss  of  nitrogen.  In  a  second  edition 
he  considered  that  the  combined  nitrogen  of  the  air 
was  sufficient  for  crop  production.  He  overestimated 
the  amount  of  ammonia  in  the  air,  and  underestimated 
the  value  of  the  nitrogen  in  soils  and  manures.  A 
study  of  the  composition  of  plant-ashes  led  him  to 
propose  the  mineral  theory  of  plant  nutrition.  De- 
Saussure  had  shown  that  plants  contained  certain 
mineral  elements,  but  he  did  not  emphasize  their  im- 
portance as  plant  food.  Liebig's  writings  on  the  com- 
position of  plant-ash,  and  the  importance  of  supplying 
crops  with  mineral  food  led  to  the  commercial  prepara- 
tion of  manures,  which  in  later  years  has  developed 
into  the  commercial  fertilizer  industry.  The  work  of 
Iviebig  was  not  conducted  in  connection  wath  field 
experiments.  It  had,  however,  a  most  stimulating 
influence  upon  investigations  in  agricultural  chemistry, 
'and  to  him  we  owe,  in  a  great  degree,  the  summari- 
zing of  previous  disconnected  work  and  the  mapping 
out  of  valuable  lines  for  future  investigations. 

Liebig's  enthusiasm  for  agricultural  investigations 
may  be  judged  from  the  following  extract  :  ''  I  shall 
be  happy  if  I  succeed  in  attracting  the  attention  of  men 


INTRODUCTION  7 

of  science  to  subjects  which  so  well  merit  to  engage 
their  talents  and  energies.  Perfect  agriadtiire  is  the 
true  foundation  of  trade  and  industry  ;  it  is  the  foun- 
datiojt  of  the  I'iches  of  states.  But  a  rational  system 
of  agriculture  cannot  be  formed  without  the  applica- 
tion of  scientific  principles ;  for  such  a  system  must  be 
based  on  an  exact  acquaintance  with  the  means  of 
nutrition  of  vegetables,  and  with  the  influence  of  soils, 
and  actions  of  manures  upon  them.  This  knowledge 
we  must  seek  from  chemistry,  which  teaches  the  mode 
of  investigating  the  composition  and  of  the  study  of 
the  character  of  the  different  substances  from  which 
plants  derive  their  nourishment."  ^ 

Soon  after  Liebig's  first  work  appeared  the  investi- 
gations at  Rothamsted  by  Sir  J.  B.  Lawes  were  under- 
taken. The  most  extensive  systematic  work  in  both 
field  experiments  and  laboratory  investigations  which 
have  ever  been  conducted  have  been  carried  on  by 
Lawes  and  Gilbert  at  Rothamsted,  Eng.  Dr.  Gilbert 
had  previously  been  a  pupil  of  Liebig,  and  his  associa- 
tion with  Sir  J.  B.  Lawes  marked  the  establishment 
of  the  second  experiment  station.  Many  of  the  Roth- 
amsted experiments  have  been  continued  since  1844, 
and  results  of  the  greatest  value  to  agriculture  have 
been  obtained.  The  investiofations  on  the  non-assimi- 
lation  of  the  atmospheric  nitrogen  by  crops,  published 
in  1 86 1,  were  accepted  as  conclusive  evidence  upon 
this  much-vexed   question.     The   work  on   manures, 


8  SOILS    AND    FERTILIZERS 

nitrification,  the  nitrogen  supply  of  crops,  and  on  the 
increase  and  decrease  of  the  nitrogen  of  the  soil  when 
different  crops  are  produced,  has  had  a  most  important 
bearing  upon  maintaining  the  fertility  of  soils. 

"  The  general  plan  of  the  field  experiments  has  been 
to  grow  some  of  the  most  important  crops  of  rotation, 
each  separately,  for  many  years  in  succession  on  the 
same  land,  without  manure,  with  farmyard  manure, 
and  with  a  great  variety  of  chemical  manures,  the 
same  kind  of  manure  being,  as  a  rule,  applied  year  after 
year  on  the  same  plot.  Experiments  with  different 
manures  on  the  mixed  herbage  of  permanent  grass 
land,  on  the  effects  of  fallow,  and  on  the  actual  course 
of  rotation  without  manure,  and  with  different  manures 
have  likewise  been  made."  '^ 

In  addition  to  Davy,  Thaer,  DeSaussure,  Bous- 
singault,  Liebig,  and  Lawes  and  Gilbert,  a  great 
many  others  have  contributed  to  our  knowledge 
of  the  chemistry  of  soils.  The  work  of  Pasteur,  while 
it  did  not  directly  relate  to  soils,  indirectly  had  a  great 
influence  upon  soil  investigations.  His  researches 
upon  fermentation  made  it  possible  for  Schlosing  to 
prove  that  nitrification  was  the  result  of  the  workings 
of  living  organisms  which  have  since  been  isolated 
and  studied  by  Warington  and  Winogradsk}-. 

Many  of  the  more  recent  in\'estigations  relating  to 
the  chemistry  of  soils  are  reviewed  in  the  following 
chapters.     Our  knowledge  regarding   the   chemistry. 


INTRODUCTION  9 

physics,  geology,  and  bacteriology  of  soils  is  at  the 
present  time  far  from  complete,  but  many  facts  have 
been  discovered  which  are  of  the  greatest  value  to  the 
practical  farmer.  Of  late  years  investigations  relating 
to  the  chemistry  of  soils  and  fertilizers  have  become 
so  extensive  that  the  term  'agronomy'  has  been  used 
to  designate  that  part  of  agricultural  chemistry. 

In  soil  investigations  it  has  frequently  happened, 
owing  to  imperfect  interpretation  of  results  and  to 
the  presence  of  man}-  modifying  influences,  that  the 
results  and  conclusions  of  one  investigator  appear  to 
be  directly  contradictory  to  those  of  another.  This 
is  well  illustrated  in  the  investigations  relating  to  the 
assimilation  of  the  free  atmospheric  nitrogen,  in  which 
seemingly  opposite  conclusions  now  form  a  complete 
theorv. 


CHAPTER  I 

PHYSICAL  PROPERTIES  OF  SOILS 

1.  Soil.  —  Soil  is  disintegrated  and  pnlverized  rock 
mixed  with  animal  and  vegetable  matter.  The  rock 
particles  are  of  different  kinds  and  sizes,  and  are  in 
varions  stages  of  decomposition.  If  two  soils  are 
formed  from  the  same  kind  of  rock  and  differ  only  in 
the  size  of  the  particles,  the  difference  is  merely  a 
physical  one.  If,  however,  one  soil  is  formed  largely 
from  sandstone,  while  the  other  is  formed  from  lime- 
stone, the  difference  is  both  physical  and  chemical. 
Hence  it  is  that  soils  differ  both  physically  and  chem- 
ically. It  is  difficnlt  to  consider  the  physical  proper- 
ties of  a  soil  withont  also  considering  the  chemical 
properties.  The  chemical  and  physical  properties  of 
a  soil,  when  jointly  considered,  determine  largely  its 
agricultnral  valne. 

2.  Physical  Properties  Defined. — The  physical 
properties  of  a  soil  are  : 

1.  Weight. 

2.  Color. 

3.  Size,  form,  and  arrangement  of  the  soil  particles. 

4.  The  relation  of  the  soil  to  water,  heat,  and  cold. 

5.  The  relation  of  the  soil  to  electricity. 

6.  Odor  and  taste. 


PHYSICAL   PROPERTIES   OF    SOILS  II 

3.  Weight.  —  Soils  differ  in  weight  according  to 
the  composition  and  size  of  the  particles.  Fine  sandy 
soils  weigh  heaviest,  while  peaty  soils  are  lightest  in 
weight.  But  when  saturated  with  water,  a  cubic  foot 
of  peaty  soil  weighs  more  than  a  cubic  foot  of  sandy 
soil.  Clay  soils  w^eigh  less  per  cubic  foot  than  sandy 
soils.  The  laro;er  the  amount  of  org^anic  matter  in  a 
soil  the  less  the  weight.  Pasture  land,  for  exam- 
ple, w^eighs  less  per  cubic  foot  than  arable  land. 
Weight  is  an  important  property  to  consider  when  the 
total  amounts  of  plant  food  in  two  soils  are  compared. 
For  example,  a  peaty  soil  containing  i  per  cent,  of 
nitrogen  and  w^eighing  30  pounds  per  cubic  foot  has 
less  total  nitrogen  than  a  soil  containing  0.40  per  cent, 
of  nitrogen  and  weighing  80  pounds  per  cubic  foot. 

(i)  The  weight  of  soils  per  cubic  foot  is  approxi- 
mately as  follows  :  ^ 

Pounds. 

Clay  soil 70  to  75 

Fine  sandy  soil 95  to  1 10 

Loam  soil 75  to  90 

Peaty  soil 25  to  60 

Average  prairie  soil  •  •  • 75 

Uncultivated  prairie  soil 65 

Figures  for  the  weight  per  cubic  foot  or  specific 
gravity  of  soils  are  on  the  basis  of  the  dry  soil.  When 
taken  from  the  field  the  weight  per  cubic  foot  varies 
with  the  amount  of  water  present. 

(2)  The  volume  of  a  soil  varies  with  the  conditions 


12  SOILS    AND    FERTILIZERS 

to  which  it  has  been  subjected.  Usually  about  50 
per  cent,  of  the  volume  of  a  soil  is  air  space.  A  cubic 
foot  of  soil  from  a  field  which  has  been  well  cultivated 
weighs  less  than  from  a  field  where  the  soil  has  been 
compacted.  Hence  it  is  that  soils  have  both  a  real 
and  an  apparent  specific  gravity.  The  apparent  spe- 
cific gravity  of  a  soil  is  sometimes  less  than  half  of  the 
real  specific  gravity.  The  specific  giavity  of  different 
soils  as  given  by  Shoen  is  as  follows  :  ^ 

specific  gravity.. 

Clay  soil 2.65 

Sandy  soil 2.67 

Fine  soil 2.71 

Humus  soil 2.53 

4.  Size  of  the  Soil  Particles.  —  The  size  of  the  soil 
particles  varies  from  those  hardh-  distinguishable  with 
the  microscope  to  coarse  rock  fragments.  The  size  of 
the  particles  determines  the  character  of  the  soil  as 
sandy,  clay,  or  loam.  The  term  'fine  earth  '  is  used  to 
designate  that  part  of  the  soil  which  passes  through  a 
sieve  with  holes  0.5  mm.  (0.02  inch)  in  diameter. 
Coarse  sand  particles  and  rock  fragments  which  fail 
to  pass  through  the  sieve  are  called  skeleton.  The 
amount  of  fine  earth  and  skeleton  is  variable.  Arable 
soils,  in  general,  contain  from  5  to  20  per  cent,  of 
skeleton. 

The  fine  earth  is  composed  of  six  grades  of  soil 
particles.     The  names  and  sizes  are  as  follows  : 


PHYSICAL    PROPERTIES    OF    SOILS  1 3 

Millimeters.  Inches. 

Medium  sand 0.5      to  0.25  0.02      to  o.oi 

Fine  sand 0.25    too.  i  o.oi       to  0.004 

Very  fine  sand o.  i       to  0.05  0.004    to  0.002 

Silt 0.05    to  O.OI  0.002    to  0.0004 

Fine  silt o.oi    to  0.005  0.0004  to  0.0002 

Clay 0.005  and  less  0.0002  and  less 

Soils  are  mechanical  mixtures  of  various  sized  par- 
ticles. In  most  soils  there  is  a  predominance  of  one 
erade,  as  clav  in  lieavv  clav  soils,  and  medium  sand 
in  sandy  soils.  No  soil,  however,  is  composed  entirely 
of  one  grade.  The  clay  particles  are  exceedingly 
small ;  it  would  take  5000  of  the  larger  ones,  if  laid 
in  a  line  with  the  edges  touching,  to  measure  an  inch, 
while  it  would  take  but  50  of  the  larger  medium  sand 
particles  to  measure  an  inch. 

5.  Clay. — The  term  clay  used  physically  denotes 
those  soil  particles  less  than  0.005  ^^^^^^'  (0.0002  inch) 
in  diameter,  without  regard  to  chemical  composition. 
As  used  in  a  physical  sense  clay  may  be  silica,  feld- 
spar, limestone,  mica,  kaolin,  or  any  other  rock  or 
mineral  w^hich  has  been  pulverized  until  the  particles 
are  less  than  0.005  mm.  in  diameter.  Chemically, 
however,  the  term  clay  is  restricted  to  one  material, 
as  will  be  explained  in  another  part  of  the  work. 
The  physical  properties  of  clay  are  well  know^n.  It 
has  the  power  of  absorbing  a  large  amount  of  water, 
and  will  remain  suspended  in  water  for  a  long  time. 
The  roiled  appearance  of  many  streams  and  lakes  is 


14  SOILS   AND    FERTILIZERS 

due  to  the  presence  of  suspended  clay  particles.  The 
amount  in  agricultural  soils  may  range  from  3  to  50 
per  cent.  Clay  soils,  if  worked  when  too  wet,  become 
puddled ;  then  percolation  cannot  take  place,  and  the 
accumulated  surface  water  must  be  removed  by  the 
slow  process  of  evaporation. 

6.  Silt. — The  silt  particles  are,  in  size,  between  sand 
and  clay.  Many  of  the  western  prairie  subsoils,  clay- 
like in  nature,  are  composed  mainly  of  silt.  The  silt 
imparts  characteristics  intermediate  to  sand  and  clay. 
While  a  clay  soil  is  nearly  impervious  to  water,  and 
w^hen  w^et  works  with  difficulty,  a  silt  soil  is  more 
permeable,  but  is  not  as  open  and  porous  as  a  sandy 
soil.  When  a  soil  containing  large  amounts  of  clay 
and  silt  is  treated  wath  water,  the  silt  settles  slowly, 
while  the  clay  remains  in  suspension.  The  fine  de- 
posit in  ditches  and  drains,  where  the  water  moves 
slowly,  is  mainly  silt. 

7.  Sand.  —  There  are  three  grades  of  sand.  The 
characteristics,  as  permeability  and  non-cohesion  of 
particles,  are  so  w^ell  known  that  they  do  not  require 
discussion.  A  soil  composed  entirely  of  sand  would 
have  little,  if  any,  agricultural  value.  Sandy  soils 
usually  contain  from  5  to  15  per  cent,  of  clay  and 
silt.  The  relative  sizes  of  sand,  silt,  and  clay  are  given 
in  the  illustration. 

^8.  Form  of  Soil  Particles.  —  Soil  particles  are  ex- 


PHYSICAL   PROPERTIES   OF   SOILS 


15 


tremely  varied  in  form.  When  examined  with  the 
microscope  they  show  the  same  diversity  as  is  observed 
in  larger  stones.  In  some  soils  the  particles  are  spher- 
ical, while  in  others    they    are  angular.     The  shape 


Fig.  I.  Medium  Sand  X  150.  Fig.  2.  Fine  Sand  X  150.  Fig.  3. 
Very  Fine  Sand  X  150.  Fig.  4.  Silt  X  3?5.  Fig.  5.  Fine  Silt  X 
325.      Fig.  6.   Clay  X  325- 

of  the  particles  is  determined  by  the  way  in  which  the 
soil  has  been  formed  and  also  by  the  nature  of  the 
rock  from  which  it  was  produced. 

The  form  and  arrangement  of  the  particles  are  im- 
portant factors  to  consider  in  dealing  with  the  water 


l6  SOILvS    AND    FERTILIZERS 

content  of  soils.  In  the  wheat  lands  of  the  Red 
River  Valley  of  the  North,  the  particles  are  small  and 
spherical,  being  formed  largely  from  limestone  rock, 
while  the  subsoil  of  the  western  prairie  regions  is 
composed  largely  of  angular  silt  particles,  which  are 
intermingled  with  clay,  forming  a  mass  containing 
only  a  minimum  of  inter  soil  spaces.  The  silt  particles 
being  angular  and  imbedded  in  the  clay,  the  soil  has 
more  the  character  of  clay  than  of  silt.  While  these 
two  soils  are  unlike  in  physical  composition,  the  form 
and  arrangement  of  the  particles  give  each  nearly  the 
same  water-holding  power.  On  account  of  a  differ- 
ence in  the  form  and  arrangement  of  the  soil  particles 
two  soils  may  have  the  same  mechanical  composition, 
and  yet  possess  materially  different  physical  proper- 
ties. In  some  soils  lo  per  cent,  of  clay  is  of  more 
value  agriculturally  than  in  other  soils.  Ten  per  cent, 
of  clay  associated  with  60  or  70  per  cent,  of  silt^ 
makes  a  good  grain  soil,  while  10  per  cent,  of  clay 
associated  largely  with  sand  makes  a  soil  poorly  suited 
to  grain  culture. 

The  classification  of  the  soil  particles  into  sand,  silt, 
and  clay  is  pureh'  an  arbitrary  one.  Various  authors 
use  these  terms  in  different  ways,  and  when  compar- 
ing soils,  reported  in  different  works,  one  may  avoid 
confusion  by  omitting  the  names  and  noting  onh'  the 
sizes  of  the  particles.  A  division  has  recently  been 
suggested  by  Hopkins  ^   in    which   the  square   root   is 


PHYSIC AI.   PROPERTIES   OF    SOILS  1 7 

often  taken  as  the  constant  ratio  between  the  grades 
of  soil  particles. 

9.  Number  of  Particles  per  Gram  of  Soil.  —  It  has 

been  estimated  that  a  gram  of  soil  contains  from 
2,000,000,000  to  20,000,000,000  soil  particles  ;  soils 
which  contain  less  than  1,700,000,000  are  unproduct- 
ive. The  number  of  particles  in  a  given  volume  of 
soil  varies  with  their  size  and  form.  According  to 
Whitney^  the  number  of  particles  per  gram  of  differ- 
ent soil  types  is  as  follows  : 

Early  truck i ,955,000,000* 

Truck  and  small  fruit 3,955,000,000 

Tobacco 6,786,000,000 

Wheat 10, 228,000,000 

Grass  and  wheat 14,735,000,000 

Limestone 19,638,000,000 

Assuming  that  the  particles  are  all  spheres,  it  is  es- 
timated that  in  a  cubic  foot  of  soil  a  surface  area  of 
from  two  to  three  and  one-half  acres  is  presented  to 
the  action  of  the  roots. 

10.  Methods  Employed  in  Separating  Soil  Particles. 

—  Sieves  with  circular  holes  0.5,  0.25,  and  o.  i  mm. 
are  emplo}ed  for  the  purpose  of  separating  the  three 
coarser  grades  of  sand.  The  sieve  a^  0.5  mm.  size,  is  con- 
nected with  the  filtering  flask  c  by  means  of  the  tube 
b^  and  the  flask  is  connected  at  point  d  with  a  suc- 
tion-pump.    Ten  grams  of  soil,  after  treatment  with 

"-'•Figures  below  sixth  place  omitted  and  ciphers  substituted. 


i8 


S3ILS    AND    FERTILIZERS 


boiling  water,  are  placed  in  the  sieve.  Water  is  passed 
through  until  the  washings  are  clear.  All  particles 
larger  than  0.5  mm.  remain  in  the  sieve,  and  after  dry- 
ing and  igniting,  are  weighed.  The  contents  of  flask  r, 
containing  the  particles  less  than  0.5  mm.,  are  then 
passed  through  a  sieve  having  holes  0.25  mm.  in 
diameter.  Finally  a  o.  10  mm.  diameter  sieve  is  used. 
The  fine  sand  and  silt  are  separated  by  gravity.  The 
fine  sand  with  some  silt  and  clay  are  read- 
ily deposited  and  the  water  containing 
the  suspended  clay  is  decanted  into  a 
second  glass  vessel.  The  residue  is  treated 
with  more  water  and  allowed  to  settle; 
this  operation  is  repeated  until  the  micro- 
scope shows  the  soil  particles  to  be  nearl)' 
all  of  one  grade. 

Clay  is  obtained  by 
evaporating  an  aliquot 
portion  of  the  washings 
or  by  determining  the 
total  per  cent,  of  the  other  grades  of  particles  and  the 
volatile  matter  and  subtracting  the  sum  from  100. 
This  is  the  Osborne  sedimentation  method  with  modi- 
fications. 9  Hilgard's'°  elutriator,  and  the  apparatus 
of  Shoen-Ma}'er  are  also  used  for  separating  the  soil 
particles. 

SOIL  TYPES 

II.  Crop  Growth  and  Physical  Properties.  —The 


FiL'-. 


Figs.  8  and  9. 


SOIL   TYPES  19 

preference  of  certain  crops  for  particular  kinds  of  soil, 
as  wheat  for  a  clay  subsoil,  potatoes  for  a  sandy  soil, 
and  corn  for  a  silt  soil,  is  due  mainly  to  the  peculiari- 
ties of  the  crop  in  requiring  definite  amounts  of  water, 
and  a  certain  temperature  for  grow^th.  These  condi- 
tions are  met  by  the  soil  being  composed  of  various 
grades  of  particles  which  enable  a  certain  amount  of 
water  to  be  retained,  and  the  soil  to  properly  respond 
to  the  influences  of  heat  and  cold.  In  considering 
soil  types,  it  should  be  remembered  that  there  are  so 
many  conditions  influencing  crop  growlh  that  the 
crop-producing  power  cannot  ahvays  be  determined  l^y 
a  mechanical  analysis  of  the  soil.  The  foUownnof 
types  have  been  found  to  hold  true  in  a  large  number 
of  cases  under  average  conditions,  but  they  do  not 
represent  what  might  be  true  of  a  case  under  special 
conditions.  For  example  a  sandy  soil  of  good  fer- 
tility in  which  the  bottom  water  is  only  a  few  feet 
from  the  surface,  may  produce  larger  grainc  rops_than 
a  clay  soil  in  which  the  bottom  water  is  at  a  greater 
depth.  In  judging  the  character  of  a  soil,  special 
conditions  must  alw^ays  be  taken  into  consideration. 
In  discussing  the  following  soil  types,  a  normal  supply 
of  plant  food  and  an  average  rainfall  are  assumed  in 
all  cases. 

12.  Potato  and  Early  Truck  Soils. — The  better 
types  of  potato  soils  are  those  which  contain  about  60 
percent,  of  medium  sand,  20  to  25  percent,  of  silt,  and 


20  SOII.S   AND    FERTILIZERS 

about  5  per  cent,  of  clay.  Soils  of  this  nature  when 
supplied  with  about  3  per  cent,  of  organic  matter  will 
contain  from  5  to  12  per  cent,  of  water.  The  best 
conditions  for  crop  growth  exist  when  the  soil  con- 
tains from  5  to  7  per  cent,  of  water.  In  a  sandy  soil 
vegetation  may  reduce  the  water  to  a  much  lower 
point  than  in  a  clay  soil.  On  account  of  sandy  soil 
giving  up  its  water  so  readily  to  growing  crops  nearly 
all  is  available,  while  on  heavy  clay,  crops  show  the 
want  of  water  when  the  soil  contains  from  7  to  8  per 
cent.,  because  the  clay  holds  the  water  so  tenaciously. 
When  potatoes  are  grown  on  soils  where  there  is  an 
abnormal  amount  of  water  the  crop  is  slow  in  matur- 
ing. For  early  truck  purposes  in  northern  latitudes, 
sandy  soils  are  the  most  suitable  because  they  wariti 
up  more  readily,  and  the  absence  of  an  abnormal 
amount  of  water  results  in  early  maturity.  Excellent 
crops  of  potatoes  are  grown  on  many  of  the  silt  soils 
of  the  west  which  have  a  materially  different  com- 
position from  the  type  given.  A  soil  may  have  all 
of  the  requisites  physically  for  the  production  of  good 
potato  and  truck  crops,  and  still  be  unproductive  on 
account  of  some  peculiarity  in  chemical  composition. 

13.  General  Truck  and  Fruit  Soils.  —  For  fruit  grow- 
ing and  general  truck  purposes  the  soil  should  contain 
more  clay  and  less  sand  than  for  early  truck  farming. 
Soils  containing  from  10  to  15  per  cent,  of  clay  and  not 
more  than   40   per  cent,   of  sand  are  best  suited  for 


SOIL    TYPES  21 

growing  small  fruits.  Such  soils  will  retain  from  lo 
to  1 8  per  cent,  of  water.  There  is  a  noticeable  differ- 
ence as  to  the  adaptability  of  different  kinds  of  fruit 
to  different  soils.  Some  fruits  thrive  on  clay  land, 
provided  the  proper  cultivation  and  treatment  are 
given.  There  is  as  nuich  diversity  of  soil,  required  for 
producing  different  fruit  crops  as  for  the  production  of 
different  farm  crops.  As  a  rule,  however,  a  silt  soil 
is  most  capable  of  being  adapted  to  the  various  con- 
ditions required  by  fruit  crops. 

14.  Corn  Soils.  —  The  strongest  types  of  corn  soils 
are  those  which  contain  from  40  to  45  per  cent,  of 
medium  and  fine  sand  and  about  15  per  cent,  of  clay. 
Corn  lands  should  contain  about  15  per  cent,  of  avail- 
able water.  Heavy  clays  produce  corn  crops  which 
mature  later  than  those  grown  on  soils  not  so  close 
in  texture.  JMany  corn  soils  contain  less  sand  and 
clay,  but  more  silt  than  the  figures  given.  If  the  soil 
contains  a  high  per  cent,  of  organic  matter,  good  corn 
crops  may  be  produced  where  there  is  less  than  twelve 
per  cent,  of  clay.  Soils  containing  a  high  per  cent,  of 
sand  are  usually  too  deficient  in  available  water  to 
produce  a  good  crop.  On  the  other  hand  heavy  clay 
soils  are  slow  in  warming  up  and  are  not  suited  to  com 
culture. 

The  strongest  types  of  corn  soils  have  the  proper 
mechanical  composition  for  the  production  of  good 
crops  of  sorghum,  cotton,  flax,  and  sugar-beets.     How- 


22  SOILS   AND    FERTILIZERS 

ever,  the  amount  of  available  plant  food  required  for 
each  crop  is  not  the  same.  The  western  prairie  soils 
which  produce  most  of  the  corn  raised  in  the  United 
States,  are  composed  largely  of  silt. 

15.  Medium  Grass  and  Grain  Soils.  — For  the  pro- 
duction of  grass  and  grain  a  larger  amount  of  water 
is  required  than  for  corn.  The  yield  of  both  is  de- 
termined largely  by  the  amount  of  water  which  the 
soil  contains.  For  an  average  rainfall  of  about  30 
inches,  good  grass  and  grain  soils  should  contain 
about  15  per  cent,  of  clay  and  60  per  cent,  of  silt. 
Such  a  soil  ordinarily  holds  from  18  to  20  per  cent. 
of  water.  Many  grass  and  grain  soils  have  less  silt 
and  more  clay.  A  soil  composed  of  about  30  per 
cent,  each  of  fine  sand,  silt,  and  clay,  would  also  be 
suitable,  mechanically,  for  general  grain  production. 
There  are  a  number  of  different  types  of  grass  and 
grain  soils,  with  different  proportional  amounts  of 
sand,  silt,  and  clay.  Silt  soils,  however,  form  the 
larger  part  of  the  grain  soils  of  the  United  States. 

16.  Wheat  Soils. — For  wheat  production,  soils  of 
a  closer  texture  are  required  than  for  general  grain 
farming.  There  are  three  classes  of  wheat  soils.  The 
first  (i  in  Fig.  10)  contains  from  30  to  50  per  cent,  of 
clay  particles,  these  being  mostly  disintegrated  lime- 
stone. The  soil  of  the  Red  River  Valley  of  the  North 
belongs  to  the  first  class  of  wdieat-producing  soils. 
The  surface  soil  contains  from  8  to  12  percent,  of  veg- 


soil.    TYPES 


23 


etable  matter  and  the  subsoil  about  25  per  cent,  of 
limestone  in  a  very  fine  state  of  division.  For  the 
production  of  wheat  the  subsoil  should  contain  20  per 
cent,  of  water.  A  crop  can,  however,  be  produced  with 
less  water,  but  a  smaller  yield  is  obtained. 


C/ay 


f/'ne 


Fig.  10.     Soil  types. 


The  second  type  of  wheat  soil  (2  in  Fig.  10)  con- 
tains less  clay  and  more  silt.  Many  prairie  subsoils 
which  produce  good  crops  of  wdieat  contain  about  20 
per  cent,  of  sand,  50  per  cent,  of  silt,  and  from  20  to 
30  per  cent,  of  clay.  Soils  of  this  class  when  w^ell 
stocked  with  moisture  in   the  spring  are  capable  of 


24  SOILS    AND    FERTILIZERS 

producing  good  crops  of  wheat,  but  are  not  able  to 
withstand  drought  so  well  as  soils  of  the  first  class. 

To  the  third  class  of  wheat  soils  (3  in  Fig.  10)  belong 
those  which  are  composed  niainh-  of  silt,  containing 
usually  75  per  cent.,  and  from  10  to  15  per  cent,  of  clay. 
The  high  per  cent,  of  fine  silt  gives  the  soil  clay-like 
properties.  Soils  of  this  class  are  adapted  to  a  great 
variety  of  crops.  For  the  production  of  wheat  on  silt 
soils  it  is  very  essential  that  a  good  supply  of  organic 
matter  be  kept  in  the  soil  so  as  to  bind  together  the 
soil  particles.  The  special  peculiarities  of  the  different 
grain  crops  as  to  soil  requirements  will  be  considered 
in  connection  with  the  food  requirements  of  crops. 

17.  Sandy,  Clay,  and  Loam  Soils.  —  In  ordinary 
agricultural  literature  the  term  'sandy,'  'clay,'  or 
'  loam  '  is  used  to  designate  the  prevailing  character  of 
the  soil.  Sandy  soils  usually  contain  90  per  cent,  or 
more  of  silica  or  chemically  pure  sand.  The  term 
light  sandy  soil  is  sometimes  used  to  indicate  that  the 
soil  is  easily  worked,  while  the  term  heavy  clay 
means  that  the  soil  offers  great  resistance  to  cultiva- 
tion. Many  soils  which  are  clay-like  in  character  are 
not  composed  very  largely  of  clay.  There  are  sub- 
soils in  the  western  states  which  have  clay-like  char- 
acteristics but  contain  only  about  15  percent,  of  clay, 
the  larger  part  of  the  soil  being  silt.  A  loam  soil  is  a 
mixture  of  sand  and  clay ;  if  clay  predominates  the 
soil  is  a  clay  loam,  while  if  sand  predominates  it  is  a 
sandy  loam. 


RELATION  OF  THE  SOIL  TO  WATER 

i8.  Amount  of  Water  Required  by  Crops.  —  Ex- 
periments have  shown  that  it  takes  from  275  to  375 
pounds  of  water  to  produce  a  pound  of  dry  matter  in 
a  grain  crop.  In  order  to  produce  an  average  acre  of 
wheat  350  tons  of  water  are  needed.  The  amount  of 
water  required  for  the  production  of  an  average  acre 
of  various  crops  is  as  follows  : " 

Average  amount.  IMiiiimum  arnount. 

Tous  water.  Tons  water. 

Clover 400                                    310 

Potatoes 400                                    325 

Wheat 350                                    300 

Oats 375                                    300 

Peas 375                                    300 

Corn 300 

Grapes 375 

Sunflowers^ 6000 

The  rainfall  during  the  time  of  growth  is  frequently 
less  than  the  amount  of  water  required  for  the  pro- 
duction of  a  crop.  An  average  rainfall  of  2  inches 
per  month  during  the  three  months  of  crop  growth 
would  be  equivalent  to  only  369  tons  of  water  per 
acre,  a  variable  part  of  which  is  lost  by  evaporation. 
Hence  it  is  that  the  rainfall  during  an  average  grow- 
ing season  is  less  than  the  amount  of  water  required, 
and  in  order  to  produce  crops,  the  water  stored  up  in 
the  soil  must  be  drawn  upon  to  a  considerable  extent. 
Inasmuch  as  the  soil's  reserve  supply  of  water  is  such 
an  important  factor  in  crop  production,  it  follows  that 


26  SOILS    AND    FERTILIZERS 

the  capacity  of  the  soil  for  storing  up  water  and  giving 
it  up  as  needed  is  a  matter  to  be  considered,  par- 
ticularly since  the  power  of  the  soil  for  absorbing 
and  retaining  water  ma}-  be  influenced  by  cultivation 
'and  manuring.  Before  discussing  the  influence  of 
cultivation  upon  the  soil  water,  the  forms  in  wdiich  it 
is  present  in  the  soil  should  be  studied.  Water  is 
present  in  soils  in  three  forms  :  (i)  bottom  water,  (2) 
capillary  water,  and  (3)  hydroscopic  water. 

19.  Bottom  Water  is  water  which  stands  in  the  soil 
at  a  general  level,  and  fills  all  the  spaces  between  the 
soil  particles.  Its  distance  from  the  surface  can  be 
told  in  a  general  way  by  the  depth  of  surface  wells. 
Bottom  water  is  of  service  to  growdng  crops  when  it  is 


Fig.  II.     Water  films  surrounding  soil  particles. 

at  such  a  depth  that  it  can  be  brought  to  the  plant 
roots  by  capillarity,  but  when  near  the  surface  so  that 
the  roots  are  immersed,  very  poor  conditions  for  crop 
growth  exist.  When  the  bottom  water  can  be  brought 
within  reach  of  the  roots  by  capillarity  a  crop 
has  an  almost  inexhaustible  supply.  In  many  soils 
known  as  old  lake  bottoms  such  conditions  exist. 


RELATION    OF    THE    SOIL   TO   WATER 


27 


20.  Capillary  Water.  —  The  water  held  in  the 
capillary  spaces  above  the  bottom  water  is  known  as 
the  capillary  water.  The  capillary  spaces  of  the  soil 
are  the  small  spaces  between  the  soil  pat  tides  in 
which  w^ater  is  held  by  surface  tension ;  that  is,  the 
force  acting  between  the  soil  and  the  w^ater  is  greater 
than  the  force  of  gravity.  If  a  series  of  glass  tubes  of 
different  diameters  be  placed  in  w^ater  it  will  be  ob- 
served that  in  the  smaller  tubes  w^ater  rises  much 
his/her  than  in  the  largfer.     The  w^ater  rises  in  all  of 


"-r*^ 


[3    LI 

Fig.  12.     Comparative  height  to  which  water  rises  in  glass  tubes. 

the  tubes  until  a  point  is  reached  w^here  the  force  of 
gravity  is  equal  to  the  force  of  surface-tension.  In 
the  smaller  tubes  surface-tension  is  greater  than  the 
force  of  gravity,  and  the  water  is  drawn  up  into  the 
tube.  In  the  larger  tubes  the  surface-tension  is  less 
and  water  is  raised  only  a  short  distance.  There 
are  present  in  the  soil  many  spaces  which  are  capable 
of  taking  up  water  in  the  same  way  as  the  small  glass 
tubes.     The  height  to  which  water  can  be  raised  by 


28  SOILS   AND    FERTILIZERS  ' 

capillarity  depends  upon  the  size  and  arrangement  of 
the  soil  particles.  Water  may  be  raised  by  capillarity 
to  a  height  of  several  feet.  Ordinarily,  however,  the 
capillary  action  of  water  is  confined  to  a  few  feet.  The 
arrangement  of  the  soil  particles  influences  greatly  the 
capillary  power  of  the  soil.  Usually  from  30  to  60  per 
cent,  of  the  bulk  of  a  soil  is  air  space :  by  compacting, 
the  air  spaces  may  be  decreased  ;  by  stirring,  the  air 
spaces  are  increased.  In  some  soils  of  a  close  texture  an 
increase  in  air  spaces  results  in  an  increase  of  capillary 
spaces  and  of  water-holding  capacity,  while  in  other 
soils,  as  coarse  sandy  soils,  increasing  the  air  spaces 
decreases  the  capillary  spaces  and  the  water-holding 
capacity.  The  best  conditions  for  crop  production 
exist  when  the  soil  contains  water  to  the  extent  of 
about  40  per  cent,  of  its  total  capacity  of  saturation. 

21.  Hydroscopic  Water.  —  By  hydroscopic  water  is 
meant  the  water  content  of  the  soil  atmosphere.  The 
air  which  occupies  the  non-capillar}'  spaces  of  the  soil 
is  charged  with  moisture  in  proportion  to  the  water  in 
the  soil.  Under  normal  conditions  the  soil  atmos- 
phere is  nearly  saturated.  When  soils  have  exhausted 
their  capillar}-  water,  the  water  in  the  soil  atmosphere 
is  correspondingly  reduced.  The  a\'ailable  supply  in 
other  forms  being  exhausted,  the  hydroscopic  water 
cannot  contribute  to  plant  growth.' 

22.  Loss  of  Water  by  Percolation.  —  Whenever  a 
soil   becomes  saturated,   percolation   or    a    downward 


RELATION    OF   THE    SOIL   TO   WATER  29 

movement  of  the  water  begins.  The  extent  to  which 
losses  by  percolation  may  occur  depends  upon  the 
character  of  the  soil  and  the  amount  of  rainfall. 
When  soils  are  covered  with  vegetation  the  losses  by 
percolation  are  less  than  from  barren  fields.  In  all 
soils  which  have  only  a  limited  number  of  capillary 
spaces  and  a  large  number  of  non-capillary  spaces,  the 
amount  of  water  which  can  be  held  above  the  bottom 
water  is  small.  From  such  soils  the  losses  by  perco- 
lation are  g^reater  than  from  soils  which  have  a  largfcr 
number  of  capillary  spaces,  and  a  smaller  number  of 
non-capillary  spaces.  In  coarse  sandy  soils  many  of 
the  spaces  are  too  large  to  be  capillary. 

If  all  of  the  water  which  falls  on  some  soils  could  be 
retained  and  not  carried  beyond  the  reach  of  crops  by 
percolation,  there  would  be  an  ample  supply  for  agri- 
cultural purposes.  To  prevent  losses  by  percolation, 
the  texture  of  the  soil  ma\-  be  changed  by  cultivation 
and  by  the  use  of  manures.  If  the  soil  is  of  very  fine 
texture,  as  a  heav}'  clay,  percolation  is  slow^,  and  before 
the  water  has  time  to  sink  into  the  soil,  evaporation 
begfins;  wath  o^ood  cultivation  the  w^ater  is  able  to 
penetrate  to  a  depth  beyond  the  immediate  influence  of 
evaporation.  Compacting  an  open  porous  soil  by 
rolling,  checks  rapid  percolation  and  pre\'ents  the 
water  from  being  carried  beyond  the  reach  of  plant 
roots.  In  order  to  prevent  excessive  losses  by  perco- 
lation, the  treatment  must  be  varied  to  suit  the  re- 
quirements of  different  soils. 


30  SOILS    AND    FERTILIZERS 

23.  Loss  of  Water  by  Evaporation. — The  factors 
which  influence  evaporation  are  temperature,  humidity, 
and  rate  of  movement  of  the  air.  When  the  air  con- 
tains but  little  moisture  and  is  heated  and  moving 
rapidly,  the  most  favorable  conditions  for  evaporation 
exist.  In  semiarid  regions  the  losses  of  water  by 
evaporation  are  much  greater  than  by  percolation. 
The  drv  air  comes  in  contact  with  the  soil,  the  soil 
atmosphere  gives  up  its  water,  and,  unless  checked  by 
cultivation,  the  subsoil  water  is  brought  to  the  surface 
by  capillarity  and  lost.  In  porous  soils,  a  greater 
freedom  of  movement  of  the  air  is  possible,  which  in- 
creases the  rate  of  evaporation.  When  the  surface  of 
the  soil  is  covered  with  a  la}'er  of  finely  pulverized 
earth,  or  with  a  mulch,  excessive  losses  by  evaporation 
cannot  take  place,  because  a  material  of  different  tex- 
ture is  interposed  between  the  soil  and  the  air. 

24.  Loss  of  Water  by  Transpiration.  —  Losses  of 
water  ma}'  also  occur  from  the  leaves  of  plants  by  the 
process  known  as  transpiration.  Helriegel  obser\'ed 
that  during  some  years  100  pounds  more  water  were 
required  to  produce  a  pound  of  dr}-  matter  than  in 
other  years,  because  of  the  difference  in  the  amount  of 
water  lost  by  transpiration.  The  loss  of  water  b}' 
evaporation  can  be  controlled  by  cultivation,  but  the 
loss  by  transpiration  can  be  only  indirectly  influ- 
enced. Hot  dry  winds  may  cause  crops  to  wilt  be- 
cause the  water  lost  by  transpiration  exceeds  the  amount 
which  the  plant  takes  from  the  soil. 


INFLUENCE    OF    CULTIVATION  3 1 

The  three  ways  in  which  crops  are  deprived  of 
water  are  by  (i)  percolation,  (2)  evaporation,  and  (3) 
transpiration.  With  proper  methods  of  cultivation, 
losses  by  percolation  and  evaporation  may  be  controlled, 
and  losses  by  transpiration  may  be  reduced. 

INFLUENCE  OF  CULTIVATION  UPON  THE  WATER    SUPPLY 

OF  CROPS 

25.  Capillarity  Influenced  by  Cultivation.  —  The 

capillarity  of  the  soil  is  subject  to  change  with  different 
methods  of  cultivation,  as  rolling  and  subsoiling,  deep 
plowing  and  shallow  surface  cultivation.  The  method  of 
cultivation  which  a  soil  should  receive  in  order  to  secure 
the  best  water  supply  for  crops  must  vary  with  the 
rainfall,  the  nature  of  the  soil,  and  the  crop  to  be  pro- 
duced. It  frequently  happens  that  the  annual  rainfall 
is  sufficient  to  produce  good  crops,  but  is  too  unevenly 
distributed.  It  is  possible,  to  a  great  extent,  to  vary 
the  cultivation  to  meet  the  water  requirements  of 
crops. 

26.  Shallow  Surface  Cultivation.  —  When  shallow 
surface  cultivation  is  practiced,  the  capillary  spaces 
near  the  surface  are  destroyed  and  the  direct  connec- 
tion of  the  subsoil  water  with  the  surface  is  broken. 
When  the  soil  particles  have  been  disturbed  and  a  layer 
of  finely  pulverized  ea-^tli  covers  the  surface,  there  is  not 
that  close  contact  which  enables  the  water  to  pass 
from  particle  to  particle.  When  evaporation  takes 
place  there  is  a  movement  of  the  subsoil  water  to  the 


32 


SOILS   AND    FERTILIZERS 


surface,  but  if  the  surface  is  covered  with  a  layer  of 
fine  earth,  the  subsoil  water  cannot  readily  pass 
through  such  a  medium,  and  evaporation  is  checked. 
Hence  shallow  surface  cultivation  conserves  the  soil 
moisture. 

The  means  by  which  surface  cultivation   is  accom- 
plished must,  of  necessity,  vary  with  the  nature  of  the 


Fig.  13.     With  surface  cultivation. 

soil.  If  a  harrow  is  used  the  pulverization  should  be 
complete.  If  a  disk  is  used  the  teeth  should  be  set  at 
an  angle,  and  not  perpendicularly,  so  as  to  prevent,  as 


Fig.  14.     Without  surface  cultivation. 

suggested  by  King,'^  the  formation  of  hard  ridges 
which  hasten  evaporation.  When  the  disk  is  set  at  an 
angle,  a  layer  of  soil  is  completely  cut  off,  and  the 
capillary  connection  with  the  subsoil  is  broken.  Sur- 
face cultivation  should  be  from  two  to  three  inches 


INFLUENCE    OF    CULTIVATION  33 

deep,  and  the  finer  the  condition  in  which  the  snrface 
soil  is  left,  the  better. 

Shallow  surface  cultivation  should  be  resorted  to  as 
a  means  of  conserving  soil  moisture.  It  can  be  prac- 
ticed in  connection  with  deep  plowing,  shallow  plow- 
ing, subsoiling,  or  rolling ;  in  fact,  it  can  be  combined 
with  any  method  of  preparing  the  land.  Shallow  sur- 
face cultivation  does  not  mean  that  the  soil  should  not 
be  previously  well  prepared  by  thorough  cultivation. 
The  following  example   shows  the  extent   to  which 

shallow    surface   cultivation   mav    conserve    the    soil 
water.  ^3 

Per  cent,  of  water  in  cornfield. 
With  .shallow  sur-        Without  shallow 
face  cultivation.        surface  cultivation. 

Soil,  depth  3  to  9  inches 14.12  8.02 

Soil,  depth  9  to  15  inches 17.21  12.38 

27.  Cultivation  after  a  Rain.  — When  evaporation 
takes  place  immediately  after  a  rain,  not  only  is  there 
a  loss  of  the  water  which  has  fallen,  but  there  may 
also  be  a  loss  of  the  subsoil  water  by  translocation,  if 
nothing  be  done  to  prevent.'^  The  following  example 
shows  the  extent  to  which  the  subsoil  water  may  be 
brought  to  the  surface. '^ 

Per  cent,  of  water. 
Surface  soil.  Subsoil. 

I  to  3  inches.  6  to  12  inches. 

Before  the  shower 9.77  18.22 

After  the  shower 22.11  16.70 

The  rainfall  was  sufficient  to  have  raised  the  water 
content  of  the  surface  soil  to  20.77  per  cent.  The 
subsoil  showed  a  loss  of  1.52  per  cent.,  while  the  sur- 


34  SOILS   AND    FERTILIZERS 

face  soil  showed  a  gain  of  1.34  per  cent,  in  addition  to 
the  water  received  from  the  shower.  If  evaporation 
begins  before  the  eqnilibrinm  is  reestablished,  there  is 
lost,  not  only  the  water  from  the  shower,  bnt  also  the 
water  which  has  been  translocated  from  the  snbsoil  to 
the  surface.  Hence  the  importance  of  shallow  surface 
cultivation  immediately  after  a  rain. 

When  a  subsoil  contains  a  liberal  supply  of  water, 
and  the  surface  soil  a  minimum  amount,  there  is  after 
an  ordinary  shower  a  movement  of  the  subsoil  water 
to  the  surface.  The  soil  particles  at  the  surface  are 
surrounded  with  films  of  water  which  thicken  at  the 
expense  of  the  subsoil  water.  Surface-tension  is  the 
cause  of  this  movement  of  the  water  to  the  surface, 
and  under  the  conditions  stated  it  is  temporarily 
greater  than  the  force  of  gravit}'. 

A  thin  hard  crust  should  never  be  allowed  to  form 
after  a  rain,  because  it  hastens  the  losses  by  evapora- 
tion, while  a  soil  mulch  formed  by  surface  cultivation 
has  the  opposite  effect. 

28.  Rolling. — The  use  of  heavy  rollers  for  com- 
pacting the  soil  is  beneficial  in  a  dry  season  on  a  soil 
containing  large  proportions  of  sand  and  silt.  Rolling 
the  land  compacts  the  soil  and  improves  the  capillary 
conditions,  enabling  more  of  the  subsoil  water  to  be 
brought  to  the  surface.  Experiments  have  shown 
that  when  land  is  rolled  the  amount  of  water  in  the 
surface  soil  is  increased.     This  increase  is,   however, 


INFI.UENCE    OF    CULTIVATION  35 

at  the  expense  of  the  subsoil  water. '^  Unless  rolled 
land  receives  surface  cultivation  excessive  losses  by 
evaporation,  due  to  improved  capillarity,  may  result. 
The  use  of  the  roller  on  cla}'  land  during  a  wet  season 
results  unfavorably.  In  man}-  localities  rolling  and 
subsequent  surface  cultivation  are  not  admissible  on 
account  of  the  drifting  of  the  soil,  caused  by  heav}' 
winds. 

29.  Subsoiling.  —  By  subsoiling  is  meant  pulveri- 
zing the  soil  immediateh'  under  the  furrow  slice. 
This  is  accomplished  with  the  subsoil  plow,  which 
simply  loosens  the  soil  without  bringing  the  subsoil  to 
the  surface.  The  object  of  subsoiling  is  to  enable  the 
land  to  retain,  near  the  surface,  more  of  the  rainfall. 
Heavy  clay  lands  are  sometimes  improved  by  occasional 
subsoiling,  but  its  continued  practice  is  not  desirable. 
For  orcharding  and  fruit-growing,  it  is  frequently  re- 
sorted to,  but  is  not  beneficial  on  soils  containing 
large  amounts  of  sand  and  silt.  Rolling  and  subsoil- 
ing are  directly  opposite  in  effect.  Soils  which  are 
improved  by  rolling  are  not  improved  by  subsoiling. 
The  additional  expense  involved  should  be  considered 
when  subsoiling  is  to  be  resorted  to.  Experiments 
have  not  as  yet  been  sufficiently  decisive  to  indicate 
the  conditions  most  favorable  for  this  practice. 

30.  Fall  Plowing  conserves  the  soil  water,  by  check- 
ing evaporation  and  leaving  the  land  in  better  condi- 
tion to  retain  moisture.     Fall  plowing  should  be  fol- 


36  SOILS   AND    FERTILIZERS 

lowed  by  surface  cultivation.  Evaporation  may  take 
place  from  unplowed  land  during  the  fall,  and  in  the 
spring  the  soil  contains  appreciably  less  water  than 
plowed  land.  By  fall  4)lowing  it  is  possible  to  carry 
over  a  water  balance  in  "Jihe  soil  from  one  year  to  the 
next. 

31.  Spring  Plowing.  — When  land  is  plowed  late  in 
the  spring  there  has  been  a  previous  loss  of  water  by 
evaporation,  and  the  soil  has  not  been  able  to  store  up 
as  much  of  the  rain  and  snow  as  if  fall  plowing  had 
been  practiced. '+  Dry  soil  is  plowed  under  and  moist 
soil  brought  to  the  surface.  This  moisture  is  readily 
lost  by  evaporation  if  surface  cultivation  is  not  em- 
ployed ;  good  capillary  connection  of  the  surface  soil 
and  subsoil  is  not  obtained,  and  the  furrow  slice  soon 
becomes  dry. 

Surface  cultivation  should  immediately  follow  both 
spring  and  fall  plowing. 

Per  cent,  of  water  ini3 
Fall  plowed  Spring  plowed 

April  25  land.  land. 

From  2  to    6  inches 24.7  22.4 

"      6  to  12      "       26.6  24.1 

"    12  to  18      '•       28.8  26.5 

Average  difference   2.37  per  cent. 

32.  Mulching.  — The  use  of  well-rotted  manure  or 
straw,  spread  over  the  surface  as  a  mulch,  prevents 
evaporation.  In  forests  the  leaves  form  a  mulch 
which  is  an  important  factor  in  maintaining  the  water 
supply.     In  order  that  a  mulch  be  effectual,  it   nnist 


INFLUENCE    OF    CULTIVATION  37 

be  compacted,  —  a  loose  pile  of  straw  is  not  a  mulch. 
In  reclaiming  lands  gullied  by  water,  mulching  is 
very  beneficial.  A  slight  mulch  may  also  be  used  to 
encourage  the  growth  of  grass  on  a  refractor^^  hillside. 
When  land  is  mulched,  evaporation  is  checked.  Sur- 
face cultivation  and  mulchings  mav  be  combined  and 
excellent  results  obtained. '3 

Per  cent,  of  water  in 
Mulched  straw- 
berry patch.  Uumulched. 

Soil  2  to    5  inches 18.12  11. 17 

"     6  to  12      "       22.18  18.14 

"  12  to  18      "       24.31  21. II 

33.  Depth  of  Plowing.  — The  depth  to  which  a  soil 
should  be  plowed  in  order  to  give  the  best  results  must, 
of  necessity,  vary  with  the  conditions.  Deep  plowing 
of  sandy  land  is  not  advisable,  particularly  in  the 
spring.  On  clay  land  deeper  plowing  should  be  the 
rule.  The  longer  a  soil  is  cultivated  the  deeper  and 
more  thorough  should  be  the  cultivation.  While 
shallow  plowing  is  admissible  on  new  prairie  land, 
deeper  cultivation  should  be  practiced  when  the  land 
has  been  cropped  for  a  series  of  years.  The  depth  of 
plowing  should  be  regulated  by  the  season.  In  the 
prairie  regions,  and  in  the  northwestern  part  of  the 
United  States,  shallow  plowing  is  more  generally  prac- 
ticed than  in  the  eastern  states.  Deep  plowing  in  the 
fall  gives  better  results  than  in  the  spring.  It  is  not 
a  wise  plan  to  plow  to  the  same  depth  every  year. 
Prof.  Roberts  says:'^  "If  plowing  is  continued  at  one 


38  SOILS   AND    FERTILIZERS 

depth  for  several  seasons,  the  pressure  of  the  imple- 
ment and  the  trampling  of  the  horses  in  time  solidify 
the  bottom  of  the  furrow,  but  if  the  plowing  is  shallow 
in  the  spring  and  deep  in  summer  and  fall,  the  objec- 
tional  hard  pan  will  be  largely  prevented." 

In  regions  of  scant  rainfall  deep  plowing  of  silt  soils 
should  be  done  only  at  intervals  of  three  or  five  years., 
With  an  average  rainfall,  deep  plowing  should  be  the 
rule  on  soils  of  close  texture.  The  depth  of  plowing 
should  be  varied  to  meet  the  requirements  of  the  crop, 
of  the  soil  and  the  amount  of  rainfall. 

34.  Permeability  of  Soils.  —  The  rapidity  with 
which  water  sinks  into  the  soil  after  a  rain  depends 
upon  the  nature  of  the  soil,  and  upon  the  cultivation 
which  it  has  received.  Shallow  surface  cultivation 
leaves  the  soil  in  good  condition  to  absorb  water. 
When  the  surface  is  hard  and  dry  a  large  per  cent,  of 
the  water  which  falls  on  rolling-  land  is  lost  bv  sur- 
face  drainage.  Soils  of  close  texture  which  contain 
but  few  non-capillary  spaces,  offer  the  greatest  resist- 
ance to  the  downward  movement  of  water. 

The  term  permeable  is  applied  to  a  soil  when  it  is 
of  such  a  texture  that  it  does  not  allow  the  water  to 
accumulate  and  clog  the  non-capillary  spaces.  Culti- 
vation may  change  the  texture  of  even  a  cla\'  soil  to 
such  an  extent  as  to  render  it  permeable.  Deep 
plowing  increases  permeability.  In  regions  of  heavy 
rains  increased  permeability  is  \'ery  desirable  for  good 


INFLUENCE    OF    CULTIVATION  39 

crop  production  on  heavy  clays.  Sandy  and  loamy 
soils  have  a  high  degree  of  permeability,  and  it  is  not 
necessar}^  that  it  should  be  increased. 

35.  Fertilizers.  —  When  water  contains  dissolved 
salts,  it  is  more  susceptible  to  the  influence  of  surface- 
tension,  and  is  more  readih'  brought  to  the  surface  of 
the  soil.  In  commercial  fertilizers  soluble  salts  are 
present.     The  beneficial  effects  of  commercial   fertili- 


Sandy  soil  without  manure. 


zers  Upon  the  moisture  content  of  soils  are  liable  to 
be  overestimated,  because  the  fertilizer  undergoes  fix- 
ation when  applied,  and  does  not  remain  in  a  soluble 
condition.  Fertilizers  containing  soluble  salts  exercise 
a  favorable  influence  upon  the  moisture  content  of 
soils,  but  the  extent  of  this  influence  has  never  been 
determined  under  field  conditions. 

36.  Farm  Manures.  —  Well-prepared  farm  manures 
exercise  a  beneficial  effect  upon  the  moisture  content  of 
soils.  When  well-rotted  manure  is  worked  into  a  soil, 
the  coarse  soil  particles  and  masses  are  bound  together, 


40 


SOILS   AND    FERTILIZERS 


and  the  non-capillar}-  spaces  are  made  capillary.  The 
free  circulation  of  the  air  which  increases  evaporation, 
is  pre\'ented  when  a  sandy  soil  is  manured.     When 


Fig.  1 6.     Sandy  soil  with  manure. 

silt  and  sandy  soils  are  manured  they  are  capable  of 
retaining  more  water,  as  shown  b}'  the  following  ex- 
ample :'3 


Fine  sandy 

soil. 

Per  cent. 


95  per  cent,  fine 

sandy  soil. 

5  per  cent. 

dry  mannre. 

Per  cent. 

42 


Capacity  for  holding  water 25 

The  manure  enables  the  soil  to  retain  more  water 
near  the  surface  and  prevents  losses  by  percolation. 
The  difference  in  moisture  content  of  manured  and  un- 
manured  land  is  particularly  noticeable  in  a  dryseason.'^ 


Sandy  soil 

Sandy  soil 

well  niannred. 

nnniannred 

Water. 

Water. 

Per  cent. 

Per  cent. 

s 10.50 

8.10 

Soil  one  to  six  inches 

Coarse  leached  manure  may  ha\e  just  the  opposite 
effect  b}'  producing  an  open  and  porous  condition  of 
the  soil. 


INFLUENCE    OF    CULTIVATION  4I 

37.  Drainage. — Good  drainage  is  very  essential  in 
order  to  proper!}-  regnlate  the  water  supply.  If  the 
water  which  falls  on  the  land  is  allowed  to  flow  over 
the  surface  and  is  not  retained  in  the  soil,  there  is  not 
sufficient  reserve  water  for  crop  growth.  The  object 
of  good  drainage  is  to  store  up  as  much  water  as  pos- 
sible in  the  subsoil  and  to  prevent  surface  accumula- 
tion and  losses.  Good  drainage  is  accomplished  by 
thorough  cultivation,  and  in  regions  of  heavy  rainfall 
by  tile  drainage.  Well-drained  land  is  warmer  in  the 
spring,  has  a  larger  reserve  store  of  water,  and  is  in 
better  condition  for  crop  growth. 

38.  Influence  of  Forest  Regions.  —  The  deforesting 
of  large  areas  near  the  source  of  rivers  has  an  injurious 
influence  upon  the  moisture  content  of  adjoining  farm 
lands.  By  cutting  over  and  leaving  barren  large  tracts, 
less  water  is  retained  in  the  soil.  Near  forest  regions 
the  air  has  a  higher  moisture  content,  due  to  the 
water  given  off  by  evaporation.  Farm  lands  adjacent 
to  deforested  districts  lose  water  more  rapidly  b}- 
evaporation,  because  the  air  is  so  much  drier.  In 
Section  24  it  was  stated  that  losses  of  water  by  trans- 
piration could  be  indirectly  influenced.  This  can  be 
accomplished  by  retaining  our  forest  lands. 

Good  drainage  in  agriculture  means  not  only  good 
drainage  for  individual  farms,  but  also  good  storage 
capacity  in  the  form  of  forest  lands,  for  the  surplus 
water  which  accumulates  near  the  sources  of  large 
rivers. 


RELATION  OF  THE  SOIL  TO  HEAT 

39.  The  Sources  of  Heat  in  soils  are  (i)  solar 
heat,  and  (2)  heat  resulting  from  chemical  action. 
Solar  heat  is  the  main  source  for  crop  produc- 
tion. The  action  of  heat  upon  soils  has  been 
studied  extensively  by  Schiibler.  The  amount  of  heat 
a  soil  is  capable  of  absorbing  depends  upon  its  texture 
and  moisture  content.  All  dark-colored  soils  have  a 
greater  power  for  absorbing  heat  than  light-colored 
ones.  From  Schiibler's  experiments  it  appears  that 
when  dry,  there  may  be  as  great  a  difference  as  8°  C, 
between  light-  and  dark-colored  soils.  When  one  set 
of  soils  was  covered  with  a  thin  white  coat  of  mag- 
nesia, and  another  set  with  lampblack,  and  exposed 
under  like  conditions,  the  temperatures  were:^ 

White  coating.  Black  coating. 

Sand 43  50 

Gypsum 43  51 

Humus 42  49 

Clay 41  48 

Loam 42  50 

The  presence  of  water  in  the  soil  modifies  the  power 
for  absorbing  heat.  A  sandy  soil  for  example  retains 
about  12  percent,  of  water,  while  a  humus  soil  retains 
35  per  cent.  The  additional  amount  of  water  in  the 
humus  soil  may  cause  the  soil  temperature  to  be  lower 
than  that  of  the  sandy  soil.  While  the  humus  soil 
absorbs  more  heat  than  the  sandy  soil,  the  heat  is  used 


RELATION    OF    THE    SOIL   TO    HEAT  43 

Up  in  evaporating  water.  A  sandy  soil  readily  warms 
lip  in  the  spring  on  account  of  the  relatively  small 
amount  of  water  which  it  contains. 

The  specific  heat  of  a  soil  is  the  amount  of  heat  re- 
quired to  raise  a  given  weight  i°  C,  as  compared  with 
the  heat  required  to  raise  the  same  weight  of  water  i°. 
The  specific  heat  of  soils  ranges  from  0.2  to  0.4. 

The  effect  of  drainage  upon  soil  temperature  is 
marked.  The  surface  of  well-drained  land  is  usually 
several  degrees  warmer  than  that  of  poorly  drained 
land.  Water  being  a  poor  conductor  of  heat  it  follows 
that  soils  which  are  saturated  are  slow  to  warm  up  in 
the  spring.  At  a  depth  of  2  or  3  feet  there  is  not  such 
a  marked  difference  in  the  temperature  of  wet  and  dry 
soils.  It  is  to  be  observ^ed  that  with  proper  systems  of 
drainage  the  surplus  water  is  removed  from  the  sur- 
face soil  and  stored  up  in  the  subsoil  for  the  future  use 
of  the  crop,  and  at  the  same  time  the  temperature  of  the 
surface  soil  is  raised,  thus  improving  the  conditions  for 
crop  growth.  The  relation  of  drainage  to  the  proper 
supply  of  water  and  temperature  for  crop  growth  is  a 
matter  which  generally  receives  too  little  consideration 
in  field  practice. 

40.  Heat  from  Chemical  Reactions  within  the 
Soil.  —  Heat  also  results  from  the  slow  oxidation  of 
the  organic  matter  of  the  soil.  When  organic  matter 
decomposes,  it  produces  heat.  A  load  of  manure,  when 
it  rots  in  the  soil,  gives  off  the  same  amount  of  heat  as 


44  SOILS   AND    FERTILIZERS 

if  it  were  burned.  Manured  land  is  usually  i°  or  2° 
warmer  in  the  spring  than  unmanured  land ;  this  is  due  to 
the  oxidation  of  the  manure.  In  an  acre  of  rich  prairie 
soil  it  has  been  estimated  that  the  amount  of  organic 
matter  which  undergoes  oxidation  produces  as  much 
heat  annually  as  would  be  produced  from  a  ton  of 
coal.^^  In  well-drained  and  well-manured  land,  the 
additional  heat  is  an  important  factor  for  stimulating 
crop  growth,  particularly  in  a  cold,  backward  spring. 
The  production  of  heat  from  manure  is  illustrated  in 
the  case  of  hotbeds  where  well-rotted  manure  is  covered 
with  soil ;  this  results  in  raising  the  temperature  of  the 
soil.  When  soils  are  well  manured,  heat  is  retained 
more  effectually.  In  the  case  of  early  frosts,  crops  on 
well-manured  land  will  often  escape. 

41.  Relation  of  Heat  to  Crop  Growth.  —  All  plant 
life  is  directly  dependent  upon  solar  heat  as  the  source 
of  energy  for  the  production  of  plant  tissue.  The 
heat  of  the  sun  is  the  main  force  at  the  plant's  dis- 
posal for  decomposing  water  and  carbon  dioxide  and 
for  producing  starch,  cellulose,  and  other  compounds. 
The  growth  of  crops  is  the  result  of  the  transformation 
of  solar  heat  into  chemical  energy  which  is  stored  up 
in  the  plant.  When  the  plant  is  used  for  fuel  or  for 
food  the  quantity  of  heat  produced  by  complete  oxida- 
tion is  equal  to  the  amount  of  heat  required  for  forma- 
tion. 


COLOR  OF  SOILS 

42.  Organic  Matter  and   Iron   Compounds. — The 

principal  materials  which  impart  color  to  soils  are  or- 
ganic matter  and  iron  compounds.  Soils  containing 
large  amounts  of  organic  matter  are  dark-colored. 
A  union  of  the  decaying  organic  matter  and  the 
mineral  matter  of  the  soil  also  produces  compounds, 
brown  or  black  in  color.  When  moist,  many  soils  are 
darker  than  when  dry,  and  soils  in  which  the  organic 
matter  has  been  kept  up  by  the  use  of  manures  are 
darker  than  unmanured  soils.'^  When  rich,  black, 
prairie  soils  lose  their  organic  matter  through  im- 
proper methods  of  cultivation  or  when  the  organic 
matter  (humus)  is  extracted  in  chemical  analysis  the 
soils  become  light-colored. 

The  red  color  of  soils  is  imparted  by  ferric  oxide, 
the  yellow  by  smaller  amounts  of  the  same  material. 
The  greenish  tinge  is  supposed  to  be  due  to  the  pres- 
ence of  ferrous  compounds,  such  soils  being  so  close  in 
texture  as  to  exclude  the  oxidizing  action  of  the  air. 
Black  and  yellow  soils  are,  as  a  rule,  the  most  produc- 
tive. Color  may  serv^e,  to  a  slight  extent,  as  an  index 
of  fertility.  The  main  reason  why  black  soils  are  so 
generally  fertile  is  because  they  contain  a  higher  per 
cent,  of  nitrogen.  Black  soils  are  occasionally  unpro- 
ductive because  of  the  presence  of  compounds  injurious 
to  vegetation. 


46  SOILS   AND    FERTILIZERS 

43.  Odor  and  Taste  of  Soils.  — Soils  containing 
liberal  amounts  of  organic  matter  have  character- 
istic odors.  The  odoriferous  properties  of  a  soil  are 
due  to  the  presence  of  aromatic  bodies  produced  by 
the  decomposition  of  organic  matter.  In  cultivated 
soils  these  bodies  have  a  neutral  reaction.  Poorly 
drained  peaty  soils  give  off  volatile  acid  compounds 
when  dried.  The  amount  of  aromatic  compounds  in 
soils  is  very  small. 

The  taste  of  soils  varies  with  the  chemical  compo- 
sition. Poorly  drained  peaty  soils  usually  have  a 
slightly  sour  taste,  due  to  the  presence  of  organic 
acids.  Alkaline  soils  have  variable  tastes  according 
to  the  prevailing  alkaline  compound.  The  taste  of 
a  soil  frequently  reveals  a  fault,  as  acidit}'  or  alka- 
limetry. 

44.  Power  of  Soils  to  Absorb  Gases.  —  All  soils  pos- 
sess, to  a  variable  extent,  the  physical  power  of  absorb- 
ing gases.  When  decomposing  animal  or  vegetable 
matter  is  mixed  with  the  soil  the  gaseous  products 
given  off  are  absorbed.  The  absorption  is  both  a 
chemical  and  a  physical  action.  The  chemical 
changes  which  occur,  as  the  absorption  of  ammonia, 
are  considered  in  the  chapter  on  fixation.  The  organic 
matter  of  the  soil  is  the  principal  agent  in  the  physical 
absorption  of  gases ;  peat,  for  example,  has  the  power 
of  absorbing  large  amounts.  This  action  is  similar 
to  that  of  a  charcoal  filter  in  removing  noxious 
gases  from  water. 


COLOR    OF    SOILS  47 

45.  Relation  of  Soils  to  Electricity.  —  There  is 
always  a  certain  amount  of  electricity  in  both  the  soil 
and  the  air.  The  part  which  it  takes  in  plant  growth 
is  not  w^ell  understood.  The  action  of  a  strong  cur- 
rent upon  the  soil  undoubtedly  results  in  a  change  in 
chemical  composition;  a  feeble  current  has  either  an 
indifferent  or  a  slightly  beneficial  effect  upon  crop 
growth.  In  order  to  change  the  composition  of  the 
soil  so  as  to  render  the  unavailable  plant  food  available, 
would  require  a  current  destructive  to  vegetation. 
When  plants  are  subjected  to  too  strong  a  current  of 
electricity,  they  wilt  and  have  all  of  the  after-appear- 
ance of  frost.  The  slightly  beneficial  action  upon 
plant  growth  is  not  sufficient  to  warrant  its  use^s  yet 
in  general  crop  production  on  account  of  cost.  The 
action  of  a  weak  current  of  electricity  upon  plants  is 
undoubtedly  physiological  rather  than  chemical,  unless 
it  be  in  the  slightly  favorable  influence  which  it  exerts 
upon  nitrification.  The  resistance  which  soils,  when 
wet,  offer  to  electricity  has  been  taken  by  Whitney  as 
the  basis  for  the  determination  of  moisture  in  soils. ^^ 

46.  Importance  of  the  Physical  Study  of  Soils. — 
From  what  has  been  said  regarding  the  ph}'sical  prop- 
erties of  soils  it  is  evident  that  such  a  study  will  give 
much  valuable  information  regarding  their  probable 
agricultural  value.  While  the  physical  properties 
should  always  be  taken  into  consideration,  they  should 
not  form  the  sole  basis  for  judging  the  character  of  a 


48  SOILS   AND    FERTILIZERS 

soil,  because  two  soils  from  the  same  locality  frequently 
have  the  same  general  physical  composition  and  still 
have  entirely  different  crop-producing  powers,  due  to 
a  difference  in  chemical  composition. 

Attempts  have  been  made  to  overestimate  the  value 
of  the  physical  properties  of  soils  and  to  explain  nearly 
all  soil  phenomena  on  the  basis  of  soil  physics.  Im- 
portant as  are  the  physical  properties  of  a  soil,  it  can- 
not be  said  that  they  are  or  more  importance  than  the 
chemical  properties.  In  fact  the  four  sciences,  chem- 
istry, physics,  geology,  and  bacteriology,  are  all  closely 
connected  and  each  contributes  its  part  to  our  knowl- 
edge of  soils. 


CHAPTER  II 

GEOLOGICAL    FORMATION  AND  CLASSIFICATION  OF  SOILS 

47.  Geological  Study  of  Soils.  —  The  geological 
study  of  a  soil  concerns  itself  with  the  past  history  of 
that  soil,  the  material  out  of  which  it  has  been  pro- 
duced, together  with  the  agencies  which  have  taken  a 
part  in  its  formation  and  distribution.  Geologically, 
soils  are  classified  according  to  the  period  in  the  earth's 
history  when  formed,  and  also  according  to  the  agen- 
cies which  have  distributed  them.  Agricultural  geology 
is  of  itself  a  separate  branch  of  agricultural  science. 
The  principles  of  soil  formation  and  soil  distribution 
should  be  understood,  because  they  have  such  an  im- 
portant bearing  upon  soil  fertility.  In  this  work,  only 
a  few  of  the  more  important  topics  of  agricultural 
geology  are  treated  in  a  general  way. 

48.  Formation  of  Soils.  —  Many  geologists  believe 
the  surface  of  the  earth  to  have  been  at  one  time  solid 
rock.  It  is  now  almost  vmiversally  held  that  soils 
have  been  formed  from  rock  by  various  agents;  as,  (i) 
heat  and  cold,  (2)  water,  (3)  gases,  (4)  micro-organisms 
and  vegetable  life.  The  disintegration  of  rock  is 
usually  effected  by  the  combined  action  of  these  vari- 
ous agents.  The  process  of  soil  formation  is  a  slow 
one  and  the  various  agents  have  been  at  work  for  an 
almost  indefinite  period. 


50  vSOILS    AND    FERTILIZERS 

49.  Action  of  Heat  and  Cold.  —  The  cooling  of  the 
earth's  surface,  followed  by  a  contraction  in  volume, 
resulted  in  the  formation  of  fissures  which  exposed  a 
larger  area  to  the  action  of  other  agents.  The  unequal 
cooling  of  the  rock  caused  a  partial  separation  of  the 
different  minerals,  resulting  in  the  formation  of  smaller 
rock  particles  from  larger  rock  masses.  This  is  well 
illustrated  by  the  familiar  splitting  and  crumbling  of 
many  stones  when  heated.  The  action  of  frost  upon 
rock  is  also  favorable  to  soil  formation.  The  freezing 
of  water  in  rock  crevices  results  in  breaking  up  the 
rock  masses,  forming  smaller  bodies.  The  force  ex- 
erted by  water  when  it  freezes  is  sufficient  to  detach 
large  rocks. 

50.  Action  of  Water.  —  Water  acts  upon  soils  both 
chemically  and  physically.  'In  its  physical  action, 
water  has  been  the  most  important  agent  that  has 
taken  a  part  in  soil  formation.  The  surface  of  rocks  has 
been  worn  away  by  moving  water  and  in  many  cases  deep 
ravines  and  canons  have  been  formed  ;  the  pulverized 
rock,  being  carried  along  by  the  water  and  deposited 
under  favorable  conditions,  forms  alluvial  soil.  This 
is  illustrated  in  the  workings  of  large  rivers  where  the 
pulverized  rock  masses  are  deposited  along  the  river 
and  at  its  mouth.  A  large  portion  of  the  soil  in 
valleys  and  river  bottoms  has  been  deposited  by  water. 
The  action  of  water  is  not  alone  confined  to  the  forma- 
tion of  soils  along  water  courses,  but  is  equally  impor- 


CLASSIFICATION    OF    SOILS  5 1 

tant  in  the  formation  of  soils  remote  from  streams  or 
lakes,  as  in  the  case  of  soils  deposited  by  glaciers. 

51.  Glacial  Action. — At  one  time  in  the  earth's 
history,  the  ice-fields  of  polar  regions  covered  much 
larger  areas  than  at  present. '^  Changes  of  climate 
caused  a  recession  of  the  ice-fields,  and  resulted  in  the 
movement  of  large  bodies  of  ice,  carrying  along  rocks 
and  frozen  soil.  The  movement  and  pressure  of  the 
ice  pulverized  the  rock  and  produced  soil.  This 
action  is  well  illustrated  at  the  present  time  where 
mountains  rise  above  the  snow  line,  and  the  ice  and 
snow  melting  at  the  base  are  replaced  by  ice  and 
snow  from  above  moving  down  the  side  of  the  moun- 
tain. When  the  glacier  receded,  stranded  ice  masses 
were  distributed  over  the  land.  These  melted  slowly 
and  by  their  grinding  action  hollowed  out  places 
which  finally  became  lakes.  The  numerous  lakes  at 
the  source  of  the  Mississippi  River  and  in  central  Min- 
nesota are  supposed  to  have  been  formed  by  glacial 
action.  The  terminal  of  a  glacier  is  called  a  moraine 
and  is  covered  with  large  boulders  which  have  not 
been  disintegrated.  The  course  of  a  glacier  is  fre- 
quently traced  by  the  markings  or  scratches  of  the 
mass  on  rock  ledges.  In  glacial  soils,  the  rocks  are 
never  angular,  but  are  smooth  because  of  the  grinding 
action  during  transportation.  The  area  of  glacial  soils 
in  the  northern  portion  of  the  United  States  is  quite 
large.      These  soils  are,  as  a  rule,  fertile   because  of 


52  SOILS    AND    FERTILIZERS 

the   pulverization    and  mixing  of    a   great  variety  of 
rock. 

52.  Chemical  Action  of  Water.  —  The  chemical 
action  of  water  has  not  taken  such  an  important 
part  in  soil  formation  as  the  physical  action.  While 
nearly  all  recks  are  practically  insoluble  in  water 
there  is  always  some  material  dissolved,  evidenced  by 
the  fact  that  all  spring-water  contains  dissolved 
mineral  matter.  When  charged  with  carbon  dioxide 
and  other  gases,  water  acts  as  a  solvent  upon  rocks. 
It  converts  many  oxides,  as  ferrous  oxide,  into  hy- 
droxides. The  chemical  action  of  water  may  result  in 
the  formation  of  new  compounds  more  soluble  or 
readily  disintegrated,  as  deposits  of  clay,  which  have 
been  produced  by  the  chemical  and  physical  action  of 
water  upon  feldspar  rock.  Limestone  is  quite  readily 
disintegrated  by  water,  which  produces  many  chemical 
changes  in  both  rocks  and  soils.  The  chemical  action 
of  fertilizers  known  as  fixation  can  take  place  only  in 
the  presence  of  water.  In  fact  water  is  necessary  for 
nearly  all  chemical  reactions  in  the  soil. 

53.  Action  of  Air  and  Gases.  —  The  part  which  air 
has  taken  in  soil  formation  has  not  been  as  prominent 
as  that  taken  by  water.  By  the  aid  of  oxygen,  carbon 
dioxide,  and  other  gases  and  vapors  in  the  air,  rock 
disintegration  is  hastened.  The  action  of  oxygen 
changes  the  lower  oxides  to  higher  forms.  All  rock 
contains  more  or  less  oxygen  in  chemical  combination. 


CLASSIFICATION    OF   SOILS  53 

The  carbon  dioxide  of  the  air  under  some  conditions 
favors  the  formation  of  carbonates.  The  disinte- 
grating action  of  air,  moisture,  and  frost  is  illustrated 
in  the  case  of  building  stones  which  in  time  crumble 
and  form  a  powder.  The  combined  action  of  air, 
moisture,  and  frost  is  called  weathering. 

54.  Action  of  Vegetation.  —  Some  of  the  lower 
forms  of  plants  as  lichens  do  not  require  soil  for 
growth,  but  are  capable  of  living  on  the  bare  surface 
of  rocks,  obtaining  food  from  the  air,  and  leaving  a 
certain  amount  of  vegetable  matter  which  under- 
goes decay  and  is  incorporated  with  the  rock  parti- 
cles, preparing  the  way  for  higher  orders  of  plants 
which  take  their  food  from  the  soil.  When  this 
vegetable  matter  decays  it  enters  into  chemical  com- 
bination with  the  pulverized  rock,  forming  humates.'^ 
The  disintegrating  action  of  plant  roots  and  vegetable 
matter  upon  rocks  has  been  an  important  factor  in 
soil  formation. 

55.  Action  of  Micro-organisms.  —  Micro-organisms, 
found  on  the  surface  and  in  the  crevices  of  rocks,  are 
considered  by  many  as  active  agents  in  bringing  about 
rock  decav.  The  nitrifvino-  org^anisms  have  taken 
an  important  part  in  rendering  soils  fertile,  and  these 
with  others  have  without  doubt- aided  in  soil  forma- 
tion. Some  of  the  organisrns  found  on  the'siirface'  of- 
rocks  are  capable  of  producing  carbonac'e6us  'matter 
out  of  the  carbon  dioxide  and  other  compounds  'of 


54  SOII^S    AND    FERTILIZERS 

the  air.^°     This    action    results    in    adding  vegetable 
matter  to  the  soil. 

56.  Combined  Action  of  the  Various  Agents.  —  In 
the  decay  of  rocks  the  various  agents  named, — water 
acting  mechanically  and  chemically,  heat  and  cold, 
air,  and  vegetation, — have  been  acting  jointly,  and  have 
produced  a  more  rapid  disintegration  than  if  each 
agent  were  acting  separately.  One  of  the  best  evi- 
dences that  soil  is  derived  from  rock  is  that  there  are 
frequently  found  in  fields  pieces  of  rock  which  are 
actually  rotten,  and,  when  crushed,  closely  resemble 
the  prevailing  soil  of  the  field.  This  is  particularly 
true  of  clay  soils  where  fragments  of  disintegrated 
feldspar  are  found  which,  when  crushed,  resemble  the 
soil  in  which  the  feldspar  was  imbedded. 

DISTRIBUTION  OF  SOILS 

57.  Sedentary  and  Transported  Soils.  — The  place 
where  a  soil  is  found  is  not  necessarily  the  place  w^here 
it  was  produced  ;  that  is,  a  soil  may  be  produced  in 
one  locality  and  transported  to  another.  Soils  are 
either  sedentary  or  transported.  Sedentary  soils  are 
those  which  occupy  the  original  position  where  they 
were  formed.  They  usualh'  have  but  little  depth  be- 
fore rock  surface  is  reached.  The  stones  in  such  soils 
have  sharp  angles  because  they  have  not  been  ground 
by  transportation.  Transported  soils  are  those 
which  have  been  formed  in  one  locality  and  carried  by 


ROCKS    AND    MINERALS  55 

various  agents  as  glaciers  and  rivers,  to  other  locali- 
ties, the  angles  of  stones  in  these  soils  being  ground  off 
during  transportation.  Transported  soils  are  divided 
into  classes  according  to  the  ways  in  which  they  have 
been  formed  ;  as,  drift  soils  produced  by  glaciers,  and 
alluvial  soils  formed  by  rivers  and  deposited  by  lakes. 
Other  agents  which  have  taken  a  part  in  soil 
transportation  are  wind  and  volcanic  action.  Many 
soils  have  been  either  formed  or  modified  by  the  wind. 
The  denuding  action  of  heavy  wind  storms  upon  many 
prairie  soils  is  well  known.  Soil  particles  are  carried 
long  distances  and  then  deposited,  forming  wind-drifted 
soils.  In  some  localities  volcanic  soils  are  found ;  they 
are  extremely  varied  in  texture  and  composition — some 
are  very  fertile  and  contain  liberal  amounts  of  alka- 
line salts  and  phosphates,  while  others  contain  so  little 
plant  food  that  they  are  sterile. 
ROCKS  AND  MINERALS  FROM  WHICH  SOILS  ARE  FORMED 

58.  Composition  of  Rock.  —  Rocks  are  composed  of 
either  a  single  mineral  or  of  a  combination  of  minerals. 
Most  of  the  common  minerals  have  a  variable  range  of 
composition,  due  to  the  fact  that  one  element  or  com- 
pound may  be  partially  or  entirely  replaced  by  another. 
Most  of  the  common  rocks  from  which  soils  have  been 
produced  are  composed  of  feldspar,  mica,  hornblende, 
and  quartz. 

59.  Quartz  and  Feldspar.  —  Quartz  is  the  principal 
constituent  of  many  rock  formations.      Pure  quartz  is 


56  SOILS   AND    FERTILIZERS 

silicic  anhydride  (SiOJ.  White  sand  is  nearly  pure 
quartz.  A  soil  formed  from  pure  quartz  would  be 
sterile.  Feldspar  is  composed  of  silica,  alumina,  and 
potash  or  soda.  Lime  may  also  be  present,  and  re- 
place a  part  or  nearly  all  of  the  soda.  If  the  mineral 
contains  soda  as  the  alkaline  constituent  it  is  known 
as  albite,  or  if  mainly  potash  it  is  called  potash  feld- 
spar or  orthoclase. 

The  members  of  the  feldspar  group  are  insoluble  in 
acids  and  before  disintegration  takes  place  are  not  ca- 
pable of  supplying  plant  food.  Potash  feldspar  contains 
from  12  to  15  per  cent,  of  potash,  none  of  which  is  of 
value  as  plant  food.  When  feldspar  undergoes  disin- 
tegration it  produces  clay.  A  soil  formed  from  feld- 
spar is  usually  well  stocked  with  potash. 

Orthoclase,  AlKSi^Og Potash  Feldspar. 

Albite,  AlNaSiyO^ Sodium  Feldspar. 

60.  Hornblende. — The  hornblende  and  augite  groups 
are  formed  by  the  union  of  magnesium,  calcium,  iron, 
and  manganese,  with  silica.  There  are  none  of  the 
members  of  the  alkali  family  in  hornblende.  The  au- 
gites  are  double  silicates  of  iron,  manganese,  calcium, 
and  magnesium.  Quite  frequently  phosphoric  acid  is 
present  in  chemical  combination  with  the  iron.  The 
members  of  this  group  are  readily  distinguished  by 
their  color  which  is  black,  brown,  or  brownish  green. 
The  hornblendes  are  insoluble  in  acids,  hence  unavail- 


ROCKS    AND    MINERALS  57 

able  as  plant  food,  and  when  disintegrated  do  not  as  a 
rnle  form  ver)-  fertile  soils. 

61.  Mica. — Mica  is  qnite  complex  in  composi- 
tion, is  an  abnndant  mineral,  and  is  composed  of  sil- 
ica, iron,  alumina,  manganese,  calcium,  magnesium, 
and  potassium.  Mica  is  a  polysilicate.  The  color 
may  be  white,  brown,  black,  or  bluish  green  owing 
to  the  absence  of  iron,  or  to  its  presence  in  various 
amounts.  The  chief  physical  characteristic  of  the 
members  of  this  group  is  the  ease  with  which  they 
are  split  into  thin  layers.  It  is  to  be  observed  that  the 
mica  group  contains  all  of  the  elements  of  both  feld- 
spar and  hornblende. 

Soils  formed  from  the  disintegration  of  mica  are 
usually  fertile  owing  to  the  variety  of  essential  ele- 
ments present.  Frequently  small  pieces  of  undecom- 
posed  mica  are  found  in  soils. 

62.  Zeolites.  —  The  zeolites  form  a  large  group  of 
secondar}'  minerals.  They  are  poh'silicates  containing 
alumina  and  members  of  the  alkali  and  lime  fami- 
lies, and  all  contain  water  held  in  chemical  combina- 
tion. They  are  soluble  in  dilute  hydrochloric  acid 
and  belong  to  the  group  of  compounds  which  are  ca- 
pable, to  a  certain  extent,  of  serving  as  plant  food.  In 
color  they  are  white,  gray,  or  red.  Zeolites  are  quite 
abundant  in  clay  and  are  an  important  factor  in  soil 
fertility.  It  is  this  group  which  takes  such  an  impor- 
tant part  in  the  process  of  fixation.     The  zeolites,  when 


58  SOILS    AND    FERTILIZERS 

disintegrated,  particularly  by  glacial  action,  form  very 
fertile  soils. 

63.  Granite  is  composed  of  quartz,  feldspar,  and 
mica.  It  is  a  very  hard  rock  and  is  slow  to  disinte- 
grate. The  different  shades  of  granite  depend  upon 
the  proportion  in  which  the  various  minerals  are  pres- 
ent. Inasmuch  as  granite  contains  so  many  minerals 
it  usually  follows  that  thoroughly  disintegrated  granite 
soil  is  very  fertile.  Pure  powdered  granite  before  un- 
dergoing disintegration  furnishes  no  plant  food.  After 
weathering,  the  plant  food  gradually  becomes  availa- 
ble. Gneiss  belongs  to  the  granite  series  but  differs 
from  true  granite  by  containing  a  larger  amount  of 
mica.  Mica  schist  contains  a  larger  amount  of  mica 
than  gneiss. 

64.  Apatite  or  Phosphate  Rock.  —  Apatite  is  com- 
posed mainly  of  phosphate  of  lime,  Ca  (PO  )^,  together 
with  small  amounts  of  other  compounds  as  fluorides 
and  chlorides.  This  mineral  is  generall)'  of  a  green 
or  yellow  color.  It  is  present  in  many  soils  and  is 
of  little  value  as  plant  food  unless  associated  with  or- 
ganic matter  or  some  soluble  salts. 

65.  Kaolin  is  chemically  pure  clay  and  is  formed  by 
the  disintegration  of  feldspar.  When  feldspar  is  de- 
composed and  is  acted  upon  by  water  the  potash  is  re- 
moved and  water  of  hydration  is  taken  up,  forming 
the  product  kaolin,  which  is  hydrated  silicate  of  alu- 
mina, Al  (SiO  )  .H^O.     Impure  varieties  of  clay  are  col- 


ROCKS    AND    MINERALS  59 

ored  red  and  yellow  on  acconnt  of  the  presence  of  iron 
and  other  impurities.  Pure  kaolin  is  white,  is  in- 
soluble in  acids,  and  is  incapable  of  supplying  any 
nourishment  to  plants.  Clay  soils  are  fertile  on  ac- 
count of  the  other  minerals  and  organic  matter  mixed 
with  the  clay  and  are  usually  w^ell  stocked  wnth  pot- 
ash because  of  the  incomplete  removal  of  the  potash 
from  the  disintegrated  feldspar.  It  is  to  be  observed 
that  the  term  clay  used  chemically  means  alu- 
minum silicate,  while  physically  it  is  any  substance,  the 
particles  of  which  are  less  than  0.005  mm.  in  diameter. 
66.  Other  Rocks  and  Minerals.  —  In  addition  to 
the  rocks  and  minerals  W'hich  have  been  discussed, 
there  are  many  others  that  contribute  to  soil  forma- 
tion, as  limestone,  which  is  calcium  carbonate  ;  dolo- 
mite, a  double  carbonate  of  calcium  and  magnesium  ; 
serpentine,  a  silicate  of  magnesium  ;  and  gypsum,  cal- 
cium sulphate. 

Chemical  Composition  of  Rocks  ^" 


S  i        £0"       «6      i^c      ^6       So      -no      Hq 
■r.tr.  <<         c-^        rr.Z        ^u        S^        li<fe        5>ffi 

Quartz 95-100     

Feldspar 55-67     20-29     0-12     i-io     i-ii      

Kaolin 46  39         14 

Apatite 53      ••••    {^l^')    "" 

Mica 40-45   12-37       5-12      1-5 

Hornblende..  40-55     0-15        

Granite 60-80  10-15        4^5      2-3      •  •    • 


CHAPTER  III 

THE  CHEMICAL  COMPOSITION  OF  SOILS 

67.  Elements  Present  in  Soils.  —  Physically  consid- 
ered, a  soil  is  composed  of  disintegrated  rock  mixed 
with  animal  and  vegetable  matter ;  chemically  consid- 
ered, the  rock  particles  are  composed  of  a  large 
number  of  simple  and  complex  compounds,  each 
compound  in  turn  being  composed  of  elements  chem- 
ically united.  Elements  unite  to  form  compounds, 
compounds  to  form  minerals,  minerals  to  form  rocks, 
and  disintegrated  rocks  form  soil.  When  rocks  decom- 
pose, the  disintegration,  except  in  a  few  cases,  is  never 
carried  to  the  extent  of  liberating  the  elements,  but 
the  process  ceases  when  the  minerals  have  been  broken 
up  into  compounds.  While  there  are  present  in  the 
crust  of  the  earth  between  65  and  70  elements,  only 
about  15  are  found  in  animal  and  plant  bodies,  and  of 
these  but  12  are  absolutely  essential.  Only  four  of 
the  elements  which  are  of  most  importance  are  at  all 
liable  to  be  deficient  in  soils.  These  four  elements 
are:  nitrogen,  phosphorus,  potassium,  and  calcium. 

68.  Classification  of  the  Elements.  —  The  elements 
found  most  abundantlv  in  soils  are  divided  into  two 
classes : 


CHEMICAL    COMPOSITION    OF    SOILS  6l 

Acid-forming  elements  Bas^e-forming  elements 

Oxygen    O  Aluminum Al 

Silicon Si  Potassium K 

Phosphorus P  Sodium Na 

Sulphur S  Calcium Ca 

Chlorine CI  Magnesium Mg 

Nitrogen N  Iron Fe 

Hydrogen H 

Boron,  fluorine,  manganese,  and  barium  are  usually 
present  in  small  amounts,  besides  others  which  may 
be  present  in  traces,  as  the  rare  elements  lithium  and 
titanium. 

For  crop  purposes  the  elements  of  the  soil  may  be 
divided  into  three  classes : 

1.  Essential  elements  most  liable  to  be  deficient  : 
nitrogen,  potassium,  phosphorus,  and  calcium. 

2.  Essential  elements  usually  abundant :  iron,  mag- 
nesium, and  sulphur. 

3.  Unnecessary  and  accidental  elements,  usually 
abundant,  as  chlorine,  silicon,  aluminum,  and  man- 
ganese. 

69.  Combination  of  Elements.  —  In  dealing  with 
the  composition  of  soils  the  percentage  amounts  of  the 
individual  elements  are  not  given,  except  in  the  case 
of  nitrogen  ;  but  instead,  the  percentage  amounts  of 
the  various  oxides.  This  is  because  the  elements  do 
not  exist  as  free  elements  in  the  soil,  but  are  combined 
with  oxygen  and  other  elements  to  form  compounds. 
When  considered  as  oxides  the  acid-  and  base-forming 
elements  may  form  various  compounds  as : 


62  SOILS   AND    FERTILIZERS 

f  Silicate 
I  Phosphate 

Calcium \  Chloride 

Sulphate 
Carbonate 

Potassium 
Sodium  . . 
Magnesium  ■ 
Iron 

The  following  reactions  will  explain  some  of  the 
more  elementary  forms  of  combinations  : 

CaO  +  SiO.,  =  CaSiO,  CaO    +  SO3  =  CaSO^ 

SCaO  +  P^Oj  =Ca3(P0,),  K^O    +  SO3  =  K,SO, 

CaO  +  SO3  =  CaSO^  Na^O  +  SO3  =  Na,SO, 

CaO  +  CO2  =  CaCO.  MgO  +  SO3  =  MgSO^ 

When  considered  as  the  oxide,  calcium  may  com- 
bine  with  any  of  the  oxides  of  the  acid-forming  ele- 
ments, as  indicated  by  the  reactions,  to  form  salts. 
Each  of  the  compounds  formed  from  the  more 
common  elements  may  have  a  separate  value  as  plant 
food,  hence  it  is  important  to  consider  the  combina- 
tions of  each  element  separately. 

ACID-FORMING  ELEMENTS 

70.  Silicon. — The  element  silicon  makes  up  from 
a  quarter  to  a  third  of  the  solid  crust  of  the  earth  and 
next  to  ox}'gen  is  the  most  abundant  element  found 
in  the  soil.  Silicon  never  occurs  in  the  vSoil  in  the 
free  state.  It  either  combines  with  oxygen  to  form 
silica  (SiO^),  or  with  oxygen  and  some  base-forming 
element  or  elements  to  form  silicates.  Silica  and  the 
various  silicates  are  by  far  the  most  abundant  com- 


ACID-FORMING    ELEMENTS  63 

pounds  present  in  the  soil.  Silicon  is  not  one  of  the 
elements  absolutely  necessary  for  plant  growth,  and 
even  if  it  were,  all  soils  are  so  abundantly  supplied 
that  it  would  not  be  necessary  to  use  it  in  fertilizers. 

71.  Double  Silicates.  —  When  two  or  more  base- 
forming  elements  are  united  with  the  silicate  radical, 
a  double  silicate  is  formed.  In  fact  the  double  sili- 
cates are  the  most  common  forms  present  in  soils. 
There  are  also  a  number  of  forms  of  silicic  acid  which 
greatly  increase  the  number  of  silicates,  and  a  study  of 
the  composition  of  soils  is  largely  a  study  of  these 
various  silicates. 

72.  Carbon  is  an  acid-forming  element  and  belongs 
to  the  same  family  as  silicon  ;  it  is  found  in  the  soil 
as  one  of  the  main  constituents  of  the  volatile  or 
organic  compounds.  Carbon  also  unites  w^ith  oxygen 
and  the  base-forming  elements,  producing  carbonates, 
as  calcium  carbonate  or  limestone.  The  carbon  of  the 
soil  takes  no  direct  part  in  forming  the  carbon  com- 
pounds of  the  plant.  It  is  not  necessary  to  apply 
carbon  fertilizers  to  produce  the  carbon  compounds  of 
plants  because  the  carbon  dioxide  of  the  air  is  the 
source  for  crop  production.  It  is  estimated  that  there 
are  30  tons  of  carbon  dioxide  in  the  air  over  every 
acre  of  the  earth's  surface.^'  The  carbon  in  the  soil  is 
an  indirect  element  of  fertilit}',  because  it  is  usually 
combined  with  elements,  as  nitrogen  and  phosphorus, 
which  are  absolutely  necessary  for  crop  growth.  yTp-^ 

'     "  OF   THK 

UNIVERSITY 


64  SOILS    AND    FERTILIZERS 

73.  Sulphur  occurs  in  all  soils  mainly  m  the  form 
of  sulphates,  as  calcium  sulphate,  magnesium  sul- 
phate, and  sodium  sulphate.  It  is  an  important  ele- 
ment of  plant  food.  There  is  generally  less  than  one- 
half  per  cent,  of  sulphuric  anhydride  in  ordinary  soils, 
but  the  amount  required  by  crops  is  small  and  there 
is  usually  an  abundance  in  all  soils. 

74.  Chlorine  is  present  in  all  soils,  generally  in 
combination  with  sodium,  as  sodium  chloride.  It  may 
be  in  combination  with  other  bases.  Soils  which  con- 
tain more  than  o.  10  per  cent,  are,  as  a  rule,  sterile.  Chlo- 
rine is  present  in  the  soil  in  soluble  forms.  It  occurs  in 
all  plants,  although  it  is  not  absolutely  necessary  for 
plant  growth,  hence  its  combination  in  fertilizers  is 
unnecessary.  Chlorine  with  sodium,  as  common  salt, 
is  sometimes  used  as  an  indirect  fertilizer. 

75.  Phosphorus,  one  of  the  essential  elements  for 
plant  growth,  is  combined  with  both  the  volatile  and 
non-volatile  elements  of  the  soil.  Plants  cannot  make 
use  of  it  in  other  forms  than  those  of  phosphates. 
Phosphorus  is  usually  present  in  the  soil  as  calcium 
phosphate,  magnesium  phosphate,  or  aluminum  phos- 
phate, and  may  also  be  combined  with  the  humus, 
forming  humic  phosphates.  The  form  in  which  the 
phosphates  are  present,  as  available  or  unavailable,  is 
an  important  factor  in  soil  fertility.  Soils  are  quite 
liable  to  be  deficient  in  phosphates,  inasmuch  as  they 
are  so  largely  drawn  upon  by  many  crops,  particularly 


ACID-FORMING    ELEMENTS  65 

grain  crops  where  the  phosphates  accumulate  in  the 
seed,  and  are  sold  from  the  farm. 

76.  Nitrogen.  —  This  element  is  present  in  soils  in 
various  forms.  As  a  mineral  constituent  it  is  combined 
with  oxygen  and  the  base-forming  elements  as  potassium, 
sodium, or  calcium,  forming  nitrates  and  nitrites,  which, 
on  account  of  their  solubility,  are  never  found  in  ordi- 
nary  soils  in  large  amounts.  Nitrogen  is  present 
mainly  in  organic  combinations,  being  associated  wdth 
carbon,  hydrogen,  and  oxygen  as  one  of  the  elements 
forming  the  organic  matter  of  soils.  Nitrogen  may 
also  be  present  in  small  amounts  in  the  form  of  am- 
monia, or  of  ammonium  salts,  derived  from  rain 
water  and  from  the  decay  of  vegetable  and  animal 
matter.  While  nitrogen  is  present  in  the  air,  in  a  free 
state,  in  large  amounts,  it  can  be  appropriated  indirectly 
as  food  in  this  form  by  only  a  limited  number  of  plants. 
For  ordinary  agricultural  crops,  particularh'  the  cere- 
als, nitrogen  must  be  supplied  through  the  soil  as  com- 
bined nitrogen.  This  element  is  the  most  expensive 
and  is  liable  to  be  the  most  deficient  of  any  of  the  ele- 
ments of  plant  food.  No  other  element  takes  such  an 
important  part  in  agriculture  or  in  life  processes. 

77.  Oxygen.  —  Oxygen  is  combined  with  both  the 
acid-  and  base-forming  elements  and  is  present  in 
nearly  all  of  the  compounds  of  the  soil.  It  has  been 
estimated  that  about  one-half  of  the  crust  of  the  earth 
is  composed  of  oxygen,  which  is  found  in    large  pro- 


66  SOILS    AND    FERTILIZERS 

portions  combined  with  silicon,  forming  silica.  That 
which  is  held  in  chemical  combination  in  the  soil 
takes  no  part  in  the  formation  of  plant  tissue.  In  ad- 
dition to  being  present  in  the  soil,  oxygen  constitutes 
eight-ninths  of  the  weight  of  water  and  about  one-fifth 
of  the  weight  of  air.  It  also  forms  about  50  per  cent, 
of  the  compounds  found  in  plants  and  animals.  Oxy- 
gen in  the  interstices  of  the  soil  is  an  active  agent  in 
bringing  about  many  chemical  changes,  as  oxidation 
of  the  organic  matter,  and  disintegration  of  the  soil 
particles. 

78.  Hydrogen.  —  This  element  is  never  found  in  a 
free  state  in  the  soil,  but  is  combined  with  carbon  and 
oxygen  as  in  animal  and  vegetable  matter,  with  oxy- 
gen to  form  water,  and  in  a  few  cases  with  some  of 
the  base  elements  to  form  hydroxides.  It  is  not  found 
in  large  amounts  in  the  soil,  and  that  which  forms  a 
part  of  the  tissues  of  plants  and  animals  comes  from 
the  hydrogen  in  water.  Hydrogen  in  the  organic 
matter  of  soils  takes  no  .part  directly  in  producing  the 
hydrogen  compounds  of  plants.  On  account  of  its 
lightness,  hydrogen  never  makes  up  a  very  large  pro- 
portion, by  weight,  of  the  composition  of  bodies. 

BASE-FORMING  ELEMENTS 

79.  Aluminum  is  present  in  the  soil  in  the  largest 
quantity  of  any  of  the  base  elements.  It  is  calculated 
that  from  6  to  10  per  cent,  of  the  solid  crust  of  the 
earth  is  aluminum.     As  previously  stated  it  is  one  of 


BASE-FORMING    ELEMENTS  67 

the  constituents  of  clay,  and  furnishes  nothing  for 
plant  growth.  Physically,  however,  the  aluminum 
compounds  take  an  important  part  in  soil  fertility. 
Aluminum  is  usually  in  combination  w4th  silica  or 
with  silica  and  some  base-forming  element,  as  iron, 
potassium,  or  sodium.  The  various  forms  of  alumi- 
num silicates  are  the  most  numerous  compounds 
present  in  soils. 

80.  Potassium  is  present  in  the  soil  mainly  in 
the  form  of  silicates,  and  is  one  of  the  elements  abso- 
lutely necessary  for  plant  growth.  The  term  potash 
(potassium  oxide,  K^O)  is  usually  employed  when  the 
potassium  compounds  are  referred  to.  The  amount 
and  form  of  the  soil  potash  have  an  important  bearing 
upon  fertility.  Potassium  is  one  of  the  three  elements 
of  plant  food  usually  supplied  in  fertilizers.  The 
form  in  which  it  is  present  in  the  soil  and  its  economic 
supply  as  plant  food,  are  important  factors  of  crop 
growth,  and  are  considered  in  detail  in  Chapter  VIII. 
The  amount  of  potash  in  soils  ranges  from  0.02  to  0.8 
per  cent.  In  a  fertile  soil  it  rarely  falls  below  0.2  per 
cent. 

81.  Calcium  is  present  in  the  soil  in  a  variety  of 
forms,  as  calcium  carbonate,  calcium  silicate,  and 
calcium  phosphate.  The  calcium  oxide  (CaO)  of 
the  soil  is  generally  spoken  of  as  the  lime  content. 
Calcium  carbonate  and  sulphate  are  important  factors 
in  imparting  fertility.     A  subsoil  with  a  good  supply 


68  SOILS   AND   FERTILIZERS 

of  lime  will  stand  heavy  cropping  and  remain  in 
excellent  chemical  and  physical  condition  for  crop 
growth.  In  a  good  soil  there  is  nsnally  0.2  of  a  per 
cent,  or  more  of  lime  mainly  as  calcinm  carbonate. 

82.  Magnesium  is  present  in  all  soils  and  is  usually 
associated  with  calcium,  forming  the  mineral  dolo- 
mite, which  is  a  double  carbonate  of  calcium  and 
magnesium.  Magnesium  may  also  be  present  in  the 
soil  in  the  form  of  magnesium  sulphate  or  magnesium 
chloride.  All  crops  require  a  certain  amount  of 
magnesia  in  some  form,  in  order  to  reach  maturity 
and  produce  fertile  seeds.  There  is  generally  in  all 
soils  an  amount  sufficient  for  crop  purposes,  hence  it  is 
not  necessary  to  consider  this  element  in  connection 
with  soil  fertility. 

83.  Sodium  is  found  in  the  soil  mainly  as  sodium 
silicate,  and  is  present  to  about  the  same  extent  as 
potassium  which  it  resembles  chemically  in  many  ways; 
it  cannot,  however,  replace  the  element  potassium. 
Inasmuch  as  sodium  takes  such  an  indifferent  part  in 
plant  nutrition  it  is  never  used  as  a  fertilizer  except  in 
an  indirect  way. 

84.  Iron  is  an  element  necessary  for  plant  food  and 
is  found  in  all  soils  to  the  extent  of  from  i  to  4  per 
cent.  Crops  require  only  a  small  amount  of  iron, 
hence  there  is  always  sufficient  for  crop  purposes. 
Iron  is  present  in  soils  in  the  form  of  oxides,  hy- 
droxides, and  silicates. 


FORMS  OF  PLANT  FOOD 


85.  Three  Classes  of  Compounds. — For  agricul- 
tural purposes,  compounds  present  in  soils  may  be 
divided  into  three  classes :  '^  The  first  class  includes 
silicates  and  other  compounds  of  potash,  soda,  lime, 
magnesia,  phosphorus,  etc.,  which  are  soluble  in  the 

This    class 


soil-water    and  in  dilute  organic    acids. 

1 

^i 


V 

o/^e/l\  J.,         ^     Aa?^ 


[XWVWWv 


23 


1/me 


^/(^/ //?JoM/e  /1h//er 


Fig.  17.     Average  composition  of  soils. 
I,  Nitrogen  ;  2.  Potash  ;  3.  Phosphoric  acid. 

represents  the  most  soluble  and  the  most  active  and 
valuable  forms  of  plant  food.  There  is  only  a  very 
small  amount  in  these  forms.  In  lOo  pounds  of  soil, 
rarely  more  than  a  few  hundredths  of  a  pound  of  any 
one  of  the  important  elements  is  soluble  in  the  soil- 
water  or  in  dilute  organic  acids. 


70  SOILS    AND    FERTILIZERS 

The  plant  food  of  the  second  class  is  in  a  somewhat 
more  insoluble  form,  and  consists  of  all  those  com- 
pounds and  silicates  which  are  soluble  in  hydrochloric 
acid  of  twenty-three  per  cent,  strength,  1.115  sp.  gr. 
This  class  of  compounds  represents  the  limit  of  the 
solvent  action  of  the  stronger  solutions  of  organic 
acids,  such  as  are  found  in  the  roots  of  plants. 

The  third  class  of  silicates  includes  all  of  those  com- 
pounds which  require  the  combined  action  of  the 
highest  heat  and  the  strongest  chemicals  and  fluxes  in 
order  to  decompose  them. 

The  first  and  second  classes  of  silicates  and  other 
compounds  are  the  only  ones  which  possess  any  value 
as  plant  food.  The  third  class,  after  undergoing  the 
combined  action  of  the  various  disintegrating  agencies 
of  nature,  may  be  changed  into  the  second  class, 
called  the  zeolitic  silicates.  In  this  second  class  are 
also  included  all  of  the  mineral  elements  combined 
with  the  humus.  As  a  rule,  not  over  fifteen  or  twenty 
per  cent,  of  the  total  soil  is  in  forms  soluble  in  hydro- 
chloric acid ;  and  of  the  more  important  elements  only 
one  to  six  per  cent,  form  a  part  of  this  fifteen.  In 
two  hundred  samples  of  soil,  the  potash,  nitrogen, 
lime,  magnesia,  phosphoric  and  sulphuric  acids, 
amounted  to  3.5  per  cent.  (Fig.  17).  In  many  fertile 
soils  the  sum  of  the  nitrogen,  phosphoric  acid,  potash, 
lime,  magnesia,  and  sulphuric  and  carbonic  anhydrides 
is  less  than  1.50  per  cent.    This  means  that  in  every  100 


FORMS    OF   PLANT  FOOD 


71 


pounds  of  soil  there  are  only  from  1.5  to  3.5  pounds  of 
matter  which  can  take  any  active  part  in  the  support 
of  a-  crop,  and  96  to  98.5  pounds  are  present  simply  as 
so  much  inert  material. 

86.  Acid-insoluble  Matter  of  Soils.  —  The  insoluble 
residue  obtained  after  digest- 
ing a  soil  with  strong  hydro- 
chloric acid,  contains  potash, 
soda,  and  limited  amounts  of 
magnesia,  and  phosphoric 
acid,  with  other  elements 
which  are  of  no  value  as 
plant  food.  If  a  seed  were 
planted  in  soil  extracted  with 
strong  hydrochloric  acid,  it 
would  make  no  growth  after 
the  reserve  food  in  the  seed 
had  been  exhausted.  A  plant 
grown  in  such  a  soil  is  shown 
in  the  illustration  (Fig.  18). 

On  the  other  hand  it  can- 
not be  said  that  all  of  the 
plant  food  soluble  in  hydro- 
chloric acid  is  equally  valu- 
able. In  fact,  the  acid  repre- 
sents more  than  the  limit  of 
the    crop's    feeding    power. 


when  there  is  not  enough  of 


Fig.  iS.     Oat  plant   grown  in 
soil  extracted,  with  hydro- 
chloric acid. 


72  SOILS  AND  FERTILIZERS 

more  soluble  forms  to  aid  in  the  first  stages  of  growth. 
In  the  following  table  the  percentage  amounts  of 
compounds  soluble  and  insoluble  in  hydrochloric  acid 
are  given :  '^ 

Wheat  Heavy  clay  Grass  aud 

soil.  soil.  grain  soil. 

Solu-    Insolu-      Solu-    Insolu-      Solu-    Insolu- 
ble in        ble  ble         ble  ble         ble 

HCl     residue  in  HCl  residue  in  HCl   residue 

Insoluble  matter.  63.07  84.77  84,08  

Potash 0.54  2.18  0.21  3.46  0.30  1.45 

Soda 0.45  3.55  0.22  2.95  o.?5  0.25 

Lime 2.44  0.36  0.48  0.16  0.51  0.35 

Magnesia 1.85  0.25  0.34  0.47  0.26  0.46 

Iron 4.18  0.78  3.76  0.72  2.56  1.07 

Alumina 7.89  5.54  6.26  5.44  2.99  9.72 

Phosphoric  acid  .  0.38  •.••  0.12  0.08  0.23  0.05 

Sulphuric  acid- . .  o.ii  0.24  0.09  0.25  0.08  0.02 

The  insoluble  matter  after  digestion  with  h}'dro- 
chloric  acid,  was  submitted  to  fusion  analysis,  and  the 
figures  given  under  insoluble  residue  represent  the 
amounts  of  potash,  soda,  etc.,  insoluble  in  acids.  In 
the  clay  soil  96  percent,  of  the  total  potash  is  in  forms 
insoluble  in  hydrochloric  acid. 

87.  Soluble  and  Insoluble  Potash  and  Phosphoric 
Acid.  —  From  the  preceding  table  it  is  to  be  observed 
that  the  larger  portion  of  the  potash  in  the  soil  is  in- 
soluble in  hydrochloric  acid.  A  soil  may  contain 
from  2  to  3  per  cent,  of  total  potash,  and  90  per  cent, 
or  more  may  be  in  such  firm  chemical  combination 
with  aluminum,  silicon,  and  other  elements,  as  to  re- 
sist  the  solvent   action   of  plant   roots.     The    larger 


FORMS    OF    PI.ANT    FOOD  73 

portion  of  the  phosphoric  acid  of  the  soil  is  soluble  in 
hydrochloric  acid.  In  some  soils,  however,  from  20 
to  40  per  cent,  is  present  in  the  third  class  of  com- 
pounds. When  a  soil  is  digested  with  hydrochloric 
acid,  the  insoluble  residue  is  usually  a  fine  gray 
powder.  Some  clay  soils  retain  their  red  color  even 
after  treatment  with  acids  showing  that  the  iron  is  in 
part  in  chemical  combination  with  the  more  complex 
silicates. 

In  order  to  decompose  the  insoluble  residue  obtained 
from  the  treatment  with  hydrochloric  acid,  fluxes,  as 
sodium  carbonate  and  calcium  carbonate,  are  employed 
which  act  upon  the  complex  silicates  at  a  high  tem- 
perature, and  produce  silicates  soluble  in  acids. 
Plants,  however,  are  unable  to  obtain  food  in  such 
complex  forms  of  chemical  combination. 

88.  How  a  Soil  Analysis  is  Made.  —  A  sample  is 
obtained  from  a  field  by  taking  several  small  samples 
to  a  depth  of  6  to  9  inches,  from  different  places,  and 
uniting  them  to  form  one  sample.  All  coarse  stones 
and  roots  are  removed  and  a  record  is  made  of  the 
amount  of  these  materials.  The  soil  is  air  dried,  the 
hard  lumps  are  crushed,  and  the  materials  passed 
through  a  sieve  with  holes  0.5  mm.  in  diameter.  Only 
the  fine  earth  is  used  for  the  chemical  analysis.  Ten 
grams  of  soil  are  weighed  into  a  soil  digestion  flask, 
and  10  cc.  hydrochloric  acid  of  1.115  sp.  gr.  are  added 
for  everv  o;ram  of  soil   used.     The   dig^estion  flask   is 


74 


SOILS    AND    FERTILIZERS 


provided  with  a  glass  stopper  which  is  connected  with 
a  condensing  tube.  The  soil  digestion  flask  is  then 
placed  in  a  hot  water-bath  and  the  di- 
gestion is  carried  on  for  twelve  hours  at 
the  temperature  of  boiling  water.  After 
the  digestion  is  completed  the  contents 
of  the  flask  are  transferred  to  a  filter  and 
separated  into  an  insoluble  part,  and  the 
acid  solution  which  contains  the  com- 
pounds of  the  various  elements.  The 
following  table  will  give  a  general  idea 
of  how  the  different  materials  are  ob- 
tained from  the  acid  solution.  This  table 
is  not  intended  as  an  outline  for  soil 
analysis,  but  simply  to  give  the  stu- 
dent of  general  chemistry  an  idea  of  how  an  analysis 
is  made. 

The  second  half  of  the  acid  solution  is  divided  into 
three  portions.  The  first  portion  is  used  for  the  deter- 
mination of  phosphoric  acid.  The  acid  is  precipitated 
with  ammonium  molybdate.  The  second  portion  is 
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and  the  carbon  dioxide  is  retained  by  absorbents  and 
weighed.  The  nitrogen  and  humus  are  determined  in 
separate  portions  of  the  original  soil. 


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76  SOILS   AND    FERTILIZERS 

89.  Value  of  Soil  Analysis.  —  Opinions  differ  as  to 
the  value  of  soil  analysis.  It  is  claimed  by  some  that 
a  chemical  anah'sis  of  a  soil  is  of  no  practical  value 
because  it  fails  to  give  the  amount  of  available  plant 
food.  A  soil  may  have,  for  example,  0.4  per  cent,  of 
potash  soluble  in  hydrochloric  acid  and  still  not 
contain  sufficient  available  potash  to  produce  a  good 
crop,  while  another  soil  may  contain  0.2  per  cent, 
of  potash  soluble  in  hydrochloric  acid  and  produce 
good  crops.  While  these  facts  are  frequently  true, 
it  does  not  necessarily  follow  that  the  chemical 
analysis  of  a  soil  is  of  no  value  because  other  sol- 
vents than  hydrochloric  acid  may  be  used  for  soil 
analysis.  Hydrochloric  acid  is  used  because  it  repre- 
sents the  limit  of  the  solvent  power  of  plants.  The 
figures  obtained  by  the  use  of  hydrochloric  acid  are 
valuable  inasmuch  as  they  indicate  whenever  an  ele- 
ment is  present  in  amounts  which  are  too  limited  to 
admit  of  crop  production.  Suppose  an  ordinary  soil 
contains  0.05  per  cent,  of  acid-soluble  potash,  this 
would  be  too  small  an  amount  to  produce  good  crops. 
The  soil  might  contain  0.5  per  cent,  and  yet  not  have 
a  sufficient  amount  of  available  potash.  Hence  it  is, 
that  in  interpreting  results,  the  hydrochloric  acid  sol- 
vent may  show  when  a  soil  is  wholly  deficient  in  any 
one  element,  as  is  sometimes  the  case,  but  it  does  not 
necessarily  show  a  deficiency  in  the  case  of  a  soil  rich 
in   acid-soluble  potash ;  this  can,  however,  be  approx- 


FORMS   OF    PLANT   FOOD  77 

imately  indicated,  by  the  use  of  other  solvents,  as  ex- 
plained in  section  90. 

The  character  of  the  soil,  as  acid,  alkaline,  or  neu- 
tral should  first  be  determined,  because  plant  food  ex- 
ists in  a  different  form  in  each  class  of  soils.  If  a  soil 
contains  from  0.3  to  0.5  per  cent,  or  more  of  lime  (as 
CaO)  and  from  o.i  to  0.4  per  cent,  of  carbon  dioxide 
(COJ,  and  is  not  strongly  alkaline,  there  is  a  reason- 
able content  of  lime  carbonate.  If,  however,  the  soil 
contains  only  o.oi  or  0.02  per  cent,  of  carbon  dioxide, 
then  the  lime  is  not  present  as  carbonate,  but  is  prob- 
ably present  as  a  silicate,  in  which  case  the  soil  may 
stand  in  need  of  a  lime  fertilizer.  A  soil  which  gives 
an  alkaline  or  neutral  reaction  and  contains  0.15  per 
cent,  of  phosphorus  pentoxide,  and  is  well  supplied  with 
organic  matter  and  lime,  is  amply  provided  with  phos- 
phoric acid,  and  under  such  conditions  the  exten- 
sive use  of  phosphate  fertilizers  is  not  required, 
except  possibly  for  special  crops.  Hilgard  states  that 
should  the  per  cent,  of  phosphoric  acid  be  as  low  as 
0.05,  there  is,  in  all  probability,  a  poverty  of  this  ele- 
ment. 

Soils  containing  less  than  0.07  per  cent,  of  total  ni- 
trogen are  usually  deficient.  A  soil  containing  as 
high  as  o.  1 5  or  o.  2  per  cent,  of  nitrogen  may  fail  to  re- 
spond to  crop  production.  Such  cases  are  generally 
due  to  some  abnormal  condition  of  the  soil,  as  a  lack 
of  alkaline  compounds  which  are  necessary  for  nitri- 


78  SOILS  AND   FERTILIZERS 

fication.     The  appearance  of  the  crop  is  the  best  indi- 
cation as  to  a  deficiency  of  nitrogen. 

A  soil  which  contains  less  than  0.15  per  cent,  of  pot- 
ash soluble  in  hydrochloric  acid  is  quite  apt  to  be  de- 
ficient. Soils  which  contain  0.5  per  cent,  or  more  of 
lime  carbonate  will  produce  good  crops  on  a  smaller 
working  supply  of  potash  than  soils  which  are  poverty- 
stricken  in  lime.  As  a  rule  the  best  agricultural  soils 
contain  from  0.3  to  0.6  per  cent,  of  potash.  Sandy 
soils  of  good  depth  may  contain  less  plant  food  than 
the  figures  given,  and  not  be  in  need  of  fertilizers. 

The  term  volatile  matter  is  sometimes  confused  with 
the  term  organic  matter.  The  volatile  matter  includes 
the  organic  matter  and  the  water  which  is  held  in 
chemical  combination  as  in  the  hydrated  silicates. 
A  soil  may  have  a  high  per  cent,  of  volatile  matter 
and  contain  very  little  organic  matter.  Indeed  all 
clays  contain  from  5  to  9  per  cent,  of  water  of  hydra- 
tion. The  per  cent,  of  humus,  as  will  be  explained 
in  the  next  chapter,  does  not  represent  all  of  the  or- 
ganic matter. 

The  best  results  are  obtained  from  soil  analyses 
when  an  extended  study  is  made  of  the  soils  of  a  lo- 
cality. Then  an  unknown  soil  of  that  locality  can  be 
compared  with  a  productive  soil  of  known  composition. 
An  isolated  soil  analysis,  like  an  isolated  analysis  of 
well  water,  frequently  fails  in  its  object  because  of  a 
lack    of    proper    normal    standards    for    comparison. 


FORMS  OF  PLANT   FOOD  79 

When  extended  series  of  soil  analyses  have  been  made, 
much  valuable  information  has  been  obtained. 

Suppose  a  soil  contains  0.40  per  cent,  of  acid-soluble 
potash  and  field  experiments  indicate  that  there  is  a 
deficiency  of  available  potash.  This  may  be  due  to 
some  abnormal  condition  of  the  soil,  as  an  insufficient 
amount  of  other  alkaline  compounds  as  calcium  car- 
bonate to  take  the  place  of  the  potash  which  has  been 
withdrawn  by  the  crop,  in  which  case  the  deficiency 
of  potash  could  be  remedied  without  purchasing  solu- 
ble potash  fertilizer,  to  become  insoluble  by  fixation 
processes.  If  a  soil  contains  only  0.04  per  cent,  of 
acid-soluble  potash,  the  purchasing  of  potash  fertili- 
zers would  be  more  necessary,  but  with  0.40  per  cent, 
of  acid-soluble  potash  the  way  is  open  to  render 
this  potash  available  for  crops.  The  various  ways  of 
rendering  acid-insoluble  potash  and  other  compounds 
available  for  crop  production,  as  by  rotation  of  crops, 
use  of  farm  manures,  use  of  lime  and  green  manures, 
or  by  different  methods  of  cultivation  have  not  been 
sufficiently  studied  as  yet  to  offer  a  solution  to  all  of 
the  problems  of  how  to  render  inert  plant  food  availa- 
ble. 

90.  Action  of  Organic  Acids  upon  Soils.  —  Dilute 
organic  acids,  as  a  one  per  cent,  solution  of  citric  acid, 
have  been  proposed  as  solvents  for  the  determination 
of  easily  available  plant  food.  It  has  been  shown  in 
the  case  of  the  Rothamsted  soils  which  have  produced 


8o  vSOILS   AND    FERTILIZERS 

50  crops  of  grain  without  manures,  and  which  are 
markedly  deficient  in  available  phosphoric  acid,  that 
a  I  per  cent,  solution  of  citric  acid  dissolved  only  0.003 
per  cent,  of  phosphoric  acid  while  the  soil  contained  a 
total  of  0.12  per  cent.  In  the  case  of  an  adjoining 
plot  which  had  received  phosphate  manures  until  the 
soil  contained  a  sufficient  amount  of  available  phos- 
phoric acid  to  produce  good  crops,  there  was  present 
0.03  per  cent,  of  phosphoric  acid  soluble  in  a  i  per 
cent,  citric  acid  solution. ^^ 

Dilute  organic  acids  are,  to  a  certain  extent,  capable 
of  showing  deficiency  of  plant  food.  A  soil  wdiich 
shows  0.03  per  cent,  of  potash  or  phosphoric  acid  sol- 
uble in  I  per  cent,  citric  acid  is,  as  a  rule,  well  stocked 
wnth  available  phosphoric  acid.  Prairie  soils  of  high 
fertility  yield  from  0.03  to  0.05  per  cent,  of  both  pot- 
ash and  phosphoric  acid  soluble  in  dilute  organic 
acids ;  soils  which  are  deficient  in  these  elements  usu- 
ally contain  less  than  o.oi  per  cent. 

The  action  of  a  single  organic  acid  of  specific 
strength  cannot  be  taken  as  the  measure  of  fer- 
tility for  all  soils  and  crops  alike,  because  different 
plants  do  not  have  the  same  amount  or  kind  of  organic 
acid  in  the  sap.  Of  the  various  organic  acids,  citric 
possesses  the  greatest  solvent  action  upon  lime, 
magnesia,  and  phosphoric  acid,  while  oxalic  acid  has 
the  strongest  solvent  action  upon  the  silicates.  Tar- 
taric  acid  appears  to  be  less  active  as  a  solvent  than 


FORMS    OF    PLANT    FOOD  Si 

either  citric  or  oxalic  acid.  The  coinbined  use  of 
dihtte  organic  acids,  as  citric  with  hydrochloric  acid  of 
1. 1 15  sp.  gr.,  will  generally  give  an  accurate  idea  of 
the  character  of  a  soil.  A  fifth-normal  solution  of 
hydrochloric  acid  has  also  been  proposed  as  a  measure 
of  the  soil's  active  phosphoric  acid,  and  has  given 
satisfactory  results.  ^^ 

The  use  of  dilute  organic  acids  renders  it  possible 
to  detect  small  amounts  of  readily  soluble  phosphoric 
acid  and  potash.  It  has  been  stated  that  when  a  soil 
has  been  manured  a  few  years  with  a  phosphate  fertil- 
izer and  brought  into  good  condition  as  to  available 
phosphoric  acid,  that  a  chemical  analysis  will  fail  to 
detect  any  difference  in  the  soil  before  or  after  the 
treatment  with  fertilizer.  In  the  case  of  hydrochloric 
acid  as  a  solvent,  this  is  true  because  an  acre  of  soil 
to  the  depth  of  one  foot  weighs  about  3,500,000  lbs. 
and  500  lbs.  of  phosphoric  acid  would  increase  the 
total  amount  of  phosphoric  acid  about  0.015  per  cent. 
When  a  dilute  organic  acid  is  used,  only  the  more 
easily  soluble  phosphoric  acid  is  dissolved,  and  this 
readily  allows  fertilized  and  unfertilized  soils  to  be 
distinguished.  The  use  of  dilute  organic  acids  and 
salts  have  shown  a  decided  difference  between  soils 
fertilized  and  unfertilized  with  potash.  ^^ 

91.  Distribution  of  Plant  Food.  —  In  studying  the 
chemical  composition  of  a  soil,  the  surface  soil  and 
the  subsoil  both  require  consideration.     It  frequently 


82  SOILS   AND    FERTILIZERS 

happens  that  the  surface  soil  and  the  subsoil  have  en- 
tirely different  chemical,  as  well  as  physical,  properties. 
This  is  particularly  true  of  the  western  prairie  soils, 
where  the  surface  soils  generally  contain  less  potash 
and  lime,  but  more  nitrogen  and  phosphoric  acid,  than 
the  subsoils.  When  jointly  considered  the  surface 
and  subsoil  have  strong  crop-producing  powers,  but  if 
considered  separately  each  would  have  weak  points. 

Since  crops  appropriate  their  food  mainly  from  the 
silt  and  clay  particles,  the  amount  of  plant  food  pres- 
ent in  these  grades  of  particles  determines  largely  the 
reserve  fertility  of  the  soil.  A  soil  in  which  70  per 
cent,  of  the  total  potash  is  present  in  the  silt  and  clay, 
is  in  better  condition  for  crop  production  than  a  sim- 
ilar soil  with  a  like  amount  of  potash  which  is  present 
mainly  in  the  sand.  Because  a  soil  has  a  given  com- 
position, it  does  not  follow  that  all  of  the  different 
grades  of  particles  have  the  same  composition.  In  fact 
the  different  grades  of  soil  particles  may  have  as  varied 
a  composition  as  is  met  with  among  different  soils.^^ 


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84  SOILS    AND    FERTILIZERS 

The  figures  under  i  give  the  composition  of  the 
particles,  while  under  2  are  given  the  results  calcu- 
lated on  the  basis  of  the  total  amount  of  each  element. 
For  example,  the  clay  contains  1.47  per  cent,  of 
potash,  while  50.8  per  cent,  of  the  total  potash  of  the 
soil  is  in  the  clay  particles. 

A  soil  ma}'  contain  a  comparatively  low-  per  cent,  of 
potash  or  phosphoric  acid,  mainly  in  the  finer  particles 
and  evenly  distributed  so  that  the  crop  is  better 
supplied  with  food  than  if  more  were  present  in 
the  larger  particles,  unevenly  distributed.  The  dis- 
tribution of  the  plant  food  in  the  soil  has  not  been  so 
extensively  studied  as  the  question  of  total  plant  food. 
Sometimes  in  judging  the  character  of  a  soil  from  a 
chemical  analysis,  a  soil  fault,  as  lack  of  potash  in  the 
surface  soil,  is  corrected  by  a  high  per  cent,  of 
the  same  element  in  the  subsoil.  The  distribution  of 
plant  food  in  both  surface  soil  and  subsoil,  as  well 
as  in  the  various  grades  of  soil  particles,  is  an  im- 
portant factor  of  fertility. 

92.  Composition  of  Typical  Soils.  —  A  few  exam- 
ples are  given,  in  tabular  form,  of  the  chemical  compo- 
sition of  soils  from  different  regions  in  the  United  States. 
On  account  of  variations  in  the  same  localities,  the 
figures  represent  the  composition  of  only  limited  areas 
of  soils.  There  have  been  made  in  the  United  States 
a  large  number  of  soil  analyses,  which  as  yet  have  not 
been  compiled  nor  studied  in  a  systematic  way. 


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FORMS    OF    PLANT    FOOD  87 

93.  Alkaline  Soils.  —  When  a  soil  contains  such  an 
excessive  amount  of  alkaline  salts  as  sodium  sulphate, 
sodium  or  potassium  carbonate  or  chloride,  as  to  be 
destructive  to  vegetation,  it  is  called  an  '  alkali  ' 
soil.  These  soils  are  found  in  semi-arid  regions,  and 
wherever  conditions  have  been  such  that  the  alka- 
line compounds  have  not  been  drained  from  the 
soil.  Occasionally  calcium  chloride  is  the  destructive 
material.  Chlorine  in  any  ordinary  combination  is 
destructive  to  vegetation  when  present  to  the  extent 
of  more  than  i  part  per  looo  parts  of  soil.  Of  the 
various  alkaline  compounds  potassium  carbonate  is  one 
of  the  most  injurious.  Sodium  sulphate  is  a  milder 
form  of  alkali.  When  evaporation  takes  place  the 
alkaline  compounds  are  deposited  as  a  coating  on  the 
surface  of  the  soil.  Many  soils  supposed  to  be  strongly 
alkaline,  because  a  white  coating  is  formed  on  the 
surface,  simply  contain  so  much  lime  carbonate  that  a 
deposit  is  formed.  Many  excellent  soils  have  been 
passed  over  as  '  alkali '  soils  when  in  reality  they  are 
limestone  soils. 

94.  Improving  *  Alkali'  Soils. ^^  —  When  a  large  tract 
of  alkali  is  to  be  brought  under  cultivation  the  amount 
of  prevailing  alkaline  compounds  should  be  determined 
by  chemical  analysis.  It  frequently  happens  that 
deep  and  thorough  cultivation  are  all  the  treatment 
that  is  necessary.  If  the  prevailing  alkali  is  sodium 
carbonate  a  dressing  of  land  plaster  may  be  applied  so 


88  SOILS   AND    FERTILIZERS 

as  to  change  the  alkali  from  sodium  carbonate  to 
sodium  sulphate,  a  less  destructive  form,  the  reaction 
being  : 

Na  CO  -f  CaSO  =  CaCO  +  Na  SO  . 

Many  shrubs,  as  greesewood,  and  weeds,  as  Russian 
thistle,  take  from  the  soil  large  amounts  of  alkaline 
matter,  and  it  is  sometimes  advisable  to  remove  a 
number  of  such  crops  so  as  to  reduce  the  alkali.  A 
slightly  beneficial  effect  is  sometimes  noticed  on  small 
'  alkali '  spots  where  the  ashes  from  straw  are  used, 
forming  potassium  silicate.  As  a  rule  ashes  are  more 
injurious  than  beneficial,  on  an  '  alkali'  soil.  Irrigation 
and  thorough  drainage,  if  continued  long  enough,  will 
effect  a  permanent  cure.  Irrigation  without  drainage 
may  cause  a  more  alkaline  condition  by  bringing  to 
the  surface  subsoil  alkali.  The  waters  from  some 
streams  and  wells  are  unsuited  for  irrigation  on  ac- 
count of  containing  too  much  alkaline  matter.  Mildly 
alkaline  soils  will  usually  repay  in  crop  production  all 
the  labor  which  is  expended  in  making  them  pro- 
ductive, and  when  brought  under  cultivation  are  fre- 
quently very  fertile  soils.  A  small  amount  of  alkaline 
compounds  in  a  soil  is  beneficial  ;  in  fact,  many  soils 
would  be  more  productive  if  they  contained  more 
alkaline  matter. 

95.  Improving  Small  Tracts  of  *  Alkali'  Land. — 
When  the  places  are  located  so  that  the}'  can  be  under- 
drained  at  comparatively  little  expense,  this  should  be 


FORMS    OF    PLANT    FOOD  89 

done,  as  it  will  prove  the  best  and  most  permanent 
way  of  removing  the  alkali.  Good  snrface  drainage 
should  also  be  provided.  Quite  frequently  a  quarter 
or  a  third  of  the  total  alkali  in  the  soil  will,  in  a  dry 
time,  be  found  near  and  on  the  surface.  In  such  cases, 
and  if  the  spots  are  small,  a  large  amount  of  alkali 
can  be  removed  by  scraping  the  surface  and  then  cart- 
ing the  scrapings  away  and  dumping  them  wdiere 
they  can  do  no  damage. 

When  preparing  an  'alkali'  spot  for  a  crop,  deep 
plowing  should  be  practiced,  so  as  to  open  up  the  soil 
and  remove  the  excess  of  alkaline  matter  from  the 
surface.  Where  manure,  particularly  horse  manure, 
can  be  obtained  these  spots  should  be  manured  very 
heavily.  The  horse  manure,  when  it  decomposes,  fur- 
nishes acid  products,  which  combine  with  the  alkaline 
salts.  The  manure  also  prevents  rapid  surface  evapora- 
tion. Oats  are  about  the  safest  grain  crop  to  seed  on 
an  '  alkali '  spot  because  the  oat  plant  is  capable  of  thri- 
ving in  an  alkaline  soil  where  many  other  grain  crops 
fail. 

'Alkali'  soils  are  usually  deficient  in  available 
nitrogen.  The  organism  which  carries  on  the  work 
of  changing  the  humus  nitrogen  to  available  forms 
cannot  thrive  in  a  strong  alkaline  solution.  In  many 
of  these  soils,  as  demonstrated  in  the  laborator}-,  nitri- 
fication cannot  take  place.  After  thorough  drainage  and 
preparation  for  a  crop,  a  few  loads  of  good  soil  from  a 


90  SOILS   AND    FERTILIZERS 

fertile  field  sprinkled  on  '  alkali '  spots  will  do  much  to 
encourage  nitrification,  by  introducing  the  nitrifying 
organisms. 

THE  ORGANIC  COMPOUNDS  OF  SOILS 

96.  Sources  of  the  Organic  Compounds  of  Soils. 

—  The  organic  compounds  of  soils  are  derived  from 
accumulated  vegetable  and  animal  matter  which  has 
been  acted  upon  by  micro-organisms.  The  organic 
matter  of  the  soil  originally  consisted  of  the  same 
compounds,  as  cellulose,  proteid  bodies,  and  organic 
acids  that  are  found  in  living  plants  and  animals.  By 
the  action  of  various  micro-organisms  the  cellulose, 
proteid  bodies,  and  other  compounds  have  undergone 
chemical  changes,  and  produced  the  organic  com- 
pounds of  the  soil  which  are  mixtures  of  animal  and 
vegetable  matter  in  various  states  of  decomposition. 
The  organic  compounds  of  the  soil  may  exist  in 
various  forms  ranging  from  cellulose  to  the  final  oxi- 
dation products  as  carbon  dioxide  and  water.  ^7 

97.  Classification  of   the  Organic  Compounds.  — 

Various  attempts  have  been  made  to  classify  the  or- 
ganic compounds  of  the  soil,  but  those  which  have 
been  described  are  without  doubt  mixtures  of  various 
bodies,  and  not  distinct  compounds.  An  old  classifi- 
cation by  Miilder^^  was  humic,  ulmic,  crenic,  and  ap- 
procrenic  acids.  This  classification  does  not  include 
any  nitrogenous  matter  containing  more  than  four  per 
cent,  nitrogen,  while  organic  matter  with  eight  to  ten 


ORGANIC    COMPOUNDS    OF    SOILS  9I 

per  cent,  and  in  soitie  cases  eighteen  per  cent,  of 
nitrogen  is  quite  frequently  met  with  ;  hence  this 
classification  is  incomplete  as  it  includes  only  a  part  of 
the  organic  compounds  of  the  soil. 

98.  Humus.  —  The  term  humus  is  employed  to 
designate  what  are  considered  to  be  the  most  active 
principles  of  the  organic  compounds.  Humus  is  the 
animal  or  vegetable  matter  of  the  soil  in  intermediate 
forms  of  decomposition.  From  different  soils,  it  is  ex- 
tremely varied  in  composition  :  in  one  soil  it  may 
have  been  derived  mainly  from  cellulose,  while  in  an- 
other it  may  have  been  derived  from  a  mixture  of  cel- 
lulose, proteid  bodies,  and  other  organic  compounds. 
The  term  humus,  unless  qualified,  is  a  very  indefinite 
one.  The  humus  given  in  the  analyses  of  soils  is  ob- 
tained by  extracting  the  soil  with  a  dilute  alkali  as 
ammonium  hydroxide,  after  treating  the  soil  with  a 
dilute  acid  to  remove  the  lime  which  renders  the 
humus  insoluble. 

99.  Humification  and  Humates.  —  When  the  ani- 
mal and  vegetable  matter  incorporated  into  soils  un- 
dergoes decomposition  there  is  a  union  of  the  organic 
compounds  and  the  base-forming  elements  of  the  soil. 
The  decaying  organic  matter  produces  organic  prod- 
ucts of  an  acid  nature.  The  organic  acids  and  the 
base-forming  products  unite  to  form  humates  or  or- 
ganic salts,  which  are  neutral  bodies.  This  process  is 
humification. '7 


92  SOILS   AND    FERTILIZERS 

Humic  acid  +  calcium  carbonate  =  calcium  humate  +  CO.^. 
Humic  acid  +  potassium  sulphate  =;  potassium  humate,  etc. 

The  fact  that  a  union  occurs  between  the  organic 
matter  and  the  soil  has  been  demonstrated  by  mixing 
with  soils  known  amounts  of.  various  organic  materials, 
as  cow  manure,  green  clover,  meat  scraps,  and  saw- 
dust, and  allowing  humification  to  go  on  for  a  year  or 
more.  After  humification  has  taken  place,  the  humus 
extracted  from  the  soil  contains  more  potash,  phos- 
phoric acid,  and  other  elements  than  were  present  in 
the  humus  of  the  original  soil  and  humus-forming 
material,  showing  that  a  chemical  union  has  taken 
place  between  the  decaying  organic  matter  and  the  soil. 
The  power  of  various  organic  substances  to  produce 
humates  is  illustrated  in  the  following  table  :^9 

Humic  phos-  Humic 

phoric  acid.  potash. 

Cow  manure  humus  :  Grams.  Grams. 

In  original  manure  and  soil 1.17  1.06 

In  final  humus  product  ( after  hu- 
mification)        1.62  1.27 

Gain  in  humic  forms 0.45  0.21 

Green  clover  humus  : 

In  original  soil  and  clover 3.21  5.26 

In  final  hunnis  product 3.74  4.93 

Gain  in  humic  forms 0.53      (Loss)  0.33 

31  eat  scrap  humus  : 

In  original  meat  scraps  and  soil.  •      1.07  0.25 

In  final  humus  product 1.18  0.36 

Gain o.  1 1  o.  1 1 


ORGANIC    COMPOUNDS    OF    SOILS  93 

Humic  phos-  Hutnic 

,       ,  ,  phoric  acid.  potash. 

Sawdust  humus :  Grams.  Grams. 

In  original  sawdust  and  soil 0.85  0.67 

In  final  humus  product 0.78  0.70 

Oat  straw  humus : 

In  original  straw  and  soil 1.02  2.42 

In  final  humus  product 1,03  2.41 

100.  Comparative  Value  and  Composition  of  Hu- 
mates.  —  The  humus  produced  from  nitrogenous 
bodies,  as  meat  scraps,  is  more  vahiable  than  that  pro- 
duced from  celkilose  bodies  as  sawdust,  because  the 
former  have  a  greater  power  of  combining  with  the 
phosphoric  acid  and  potash  of  the  soil.  The  non- 
nitrogenous  compounds,  as  cellulose,  starch,  and  sugar, 
undergo  fermentation  but  seem  to  possess  little,  if  any, 
power  to  form  humates.  There  is  also  a  great  differ- 
ence in  soils  as  to  their  humus-producing  powers. 
Soils  deficient  in  lime  or  alkaline  compounds  possess 
only  a  feeble  power  to  produce  humates.  There  is 
also  a  marked  variation  in  the  composition  of  the 
humus  produced  from  different  kinds  of  organic  matter. 
Straw,  sawdust,  and  sugar,  materials  rich  in  cellulose 
and  other  carbohydrates,  yield  a  humus  characteris- 
tically rich  in  carbon  and  poor  in  nitrogen.  Materials 
rich  in  nitrogen,  like  meat  scraps,  green  clover,  and 
manure,  produce  a  more  valuable  humus,  rich  in  nitro- 
gen and  possessing  the  power  to  combine  with  the 
potash  and  phosphoric  acid  of  the  soil  to  form 
humates. 


29 


94  SOILS   AND    FERTILIZERS 

Composition  of  Humus  Produced  by 

Cow      Green      Meat     Wheat       Oat  Saw- 

manure,  clover,    scraps,     flour.      straw.       Uust.    Sugar, 

Carbon 41.95  54.22  4S.77  51.02  54.30  49.28  57.84 

Hydrogen 6.26  3.40  4.30  3.S2  2.48  3.33  3.04 

Nitrogen 6.16  8.24  10.96  5.02  2.50  0.32  0.08 

Oxygen 45.63  34.14  35.97  40.14  40.72  47-07  39-04 

Total 100.00  100.00  100.00  100.00  100.00  100.00  100.00 

Highest.                                  Lowest.  Difference. 

Carbon 57-84     Sugar 41-95  Cow  manure- .  •    15.89 

Hydrogen  ...     6.26     Cow  manure  •     2.48     Oat  straw 3.78 

Nitrogen 10.96     Meat  scraps..     0.08     Sugar 10.88 

Oxygen 47.07     Sawdust 34.14  Green  clover.  . .   12.93 

The  differences  in  composition  are  noticeable.  The 
humus  produced  by  each  material  as  green  clover,  oat 
straw,  or  sawdust  is  different  from  that  produced  -by 
any  other  material.  The  humus  from  green  clover  is 
undoubtedly  very  complex  in  nature,  because  it  con- 
tains both  nitrogenous  and  non-nitrogenous  cfbm- 
pounds,  and  each  class  has  a  different  action  in  humi- 
fication  processes,  hence  it  follows  that  the  humus 
from  the  green  clover  must  be  a  complex  mixture  of 
both  nitrogenous  and  non-nitrogenous  bodies. 

The  nature  of  the  humus,  whether  nitrogenous  or 
non-nitrogenous,  is  important.     Humus  produced  from 
sawdust  and  humus  from  meat  scraps  may  be  taken 
respectively    as  types  of    non-nitrogenous  and  nitrog-. 
enous  humus. 

loi.  Value  of  Humates  as  Plant  Food. — Various 
opinions  have  been  held  regarding  the  actual  value, 


ORGANIC    COMPOUNDS    OF    SOILS  95 

as  plant  food,  of  this  product  from  partialh*  decayed 
animal  and  vegetable  matter.  Humus  was  formerly 
regarded  as  composed  only  of  carbon,  hydrogen,  and 
oxygen,  and  inasmuch  as  plants  obtain  these  elements 
from  water  and  from  the  carbon  dioxide  of  the  air,  no 
value  was  assigned  to  humus.  Later  investigators 
added  nitrogen  to  the  list  but  stated  that  the  nitrogen, 
when  combined  with  the  humus  and  before  under- 
going fermentation,  was  of  no  value  as  plant  food. 

Recent  investigations  have  proved  that  the  phos- 
phoric acid  and  other  mineral  elements  combined 
with  the  organic  matter  of  soils  are  of  value  as  plant 
food,'^  and  it  has  been  demonstrated  that  crops  grown 
on  the  black  soils  of  Russia  obtain  a  large  part  of 
their  mineral  food  from  organic  combinations. ^3  Qui. 
ture  experiments  have  shown  that  under  normal 
conditions  plants  like  oats  and  rye  may  obtain  their 
mineral  food  entirely  from  humate  sources.  Seeds 
when  planted  in  a  mixture  of  pure  sand  and  neu- 
tral humates  from  fertile  soils,  produced  normal 
plants.  In  order  to  secure  the  best  conditions 
for  growth,  a  little  lime  must  be  present  to  prevent 
the  formation  of  humic  acid,  and  the  usual  organisms 
found  in  fertile  fields  must  also  be  introduced.  The 
following  example  is  given  of  oats  grown  under  such 
conditions  : 


96  SOILS    AND    FERTILIZERS 

Nitrogen  and  Ash  Elements.  ^^ 

In  six  oat  In  six  mature 

seeds.  plants. 

Gram.  Gram. 

Nitrogen 0.0040  0.0556 

Potash 0.0013  0.0640 

Soda o.oooi  -^.0079 

Lime 0.0002  0.0249 

Magnesia 0.0005  o-oi  10 

Iron 0.0064 

Phosphoric  anhydride 0.0016  0.0960 

Sulphuric  anhydride o.oooi  0.0090 

Silicon 0.0026  0.7300 

The  fact  that  plants  feed  on  hiimate  compounds, 
and  that  decaying  animal  and  vegetable  matter  pro- 
duce humates  from  the  inert  potash  and  phosphoric 
acid  of  the  soil,  has  an  important  bearing  upon  crop 
production,  because  it  indicates  a  way  by  which  inert 
plant  food  may  be  converted  into  more  active  fonns. 
It  also  explains  that  stable  manure  is  valuable  because 
it  makes  the  inert  plant  food  of  the  soil  more  available. 

102.  Amount  of  Plant  Food  in  Humate  Forms. — 
In  a  prairie  soil  containing  three  and  five-tenths  per 
cent,  of  hmnus  there  are  present  100,000  pounds  of 
humus  per  acre.  Combined  with  this  humus  there 
are  from  1,000  to  1,500  pounds  each  of  phosphoric 
acid  and  potash.  Soils  which  have  been  under  long 
cultivation  without  the  restoration  of  any  humus 
contain  from  300  to  500  pounds  each  of  humic  potash 
and  phosphoric  acid.'^  A  decline  in  crop-producing 
power  has  in  many  cases  been  brought  about  by  the 
destruction  of  the  humus. 


ORGANIC    COMPOUNDS    OF    SOILS  97 

103.  Loss  of  Humus.  —  The  loss  of  humus  from  the 
soil  is  caused  by  oxidation  and  by  fires.  Any  method 
of  cultivation  which  accelerates  oxidation  reduces  the 
humus  content.  In  man}-  of  the  western  prairie  soils 
which  have  been  under  continuous  grain  cultivation 
for  thirty  years  and  more,  the  amount  of  humus  has 
been  reduced  one-half.  Summer  fallowing  also  causes 
a  loss  of  humus.  When  land  is  continualh'  under 
the  plow,  and  no  manures  are  used,  the  humus  is 
rapidly  oxidized,  and  there  is  left,  in  the  soil,  organic 
matter  which  is  slow  to  decay. 

Forest  and  prairie  fires  have  been  very  destructive 
to  the  organic  compounds  of  the  soil.  A  soil  from 
Hinckley,  Minn.,  before  the  great  forest  fire  of  1893 
showed  1.69  per  cent,  humus  and  0.12  per  cent, 
nitrogen. '7  After  the  fire  there  were  present  0.41 
per  cent,  humus  and  0.03  per  cent,  nitrogen.  The 
forest  fire  caused  a  loss  of  2,500  pounds  of  nitrogen 
per  acre.  In  clearing  new^  land,  particularly  forest 
land,  there  is  frequently  an  unnecessary  destruction  of 
humus  materials.  Instead  of  burning  all  of  the  vege- 
table matter  it  would  be  better  economy  to  leave  some 
in  piles  for  future  use  as  manure.  When  all  of  the 
vegetable  matter  has  been  burned  two  or  three  good 
crops  are  obtained  but  the  permanent  crop-producing 
power  of  the  land  is  reduced  because  of  the  loss 
of  nitrogen.  When  the  vegetable  matter  has  been 
only    partially    removed    the    crops    at    first    may  be 


98  SOILS   AND    FERTILIZERS 

smaller,  but  in  a  few  years  returns  will  be  greater  than 
if  all  of  the  vegetable  matter  were  burned. 

104.  Physical  Properties  of  Soils  Influenced  by- 
Humus. —  The  physical  properties  of  a  soil  may  be 
entirely  changed  by  the  addition  or  the  loss  of  humus. 
The  influence  of  humus  upon  the  weight,  color, 
water,  and  heat  of  soils,  is  discussed  in  the  chapter  on 
the  physical  properties  of  soils.  Soils  reduced  in 
humus  content  have  less  power  of  storing  up  water 
and  resisting  drought.  This  fact  is  illustrated  in  the 
following  table  :^° 

Per  Cent.  Water. 

After  10  hours 
exposure  iu 
In  soil.        tray,  to  sun. 

Soil  rich  in  humus  (3.75  per  cent.) 16.48  6.12 

Adjoining  soil  poorer  in  humus  (  2.50  per  cent.)   12.14  3-94 

105.  Humic  Acid.  —  In  the  absence  of  calcium 
carbonate  or  other  alkaline  compounds,  the  vegetable 
matter  may  produce  acid  products  destructive  to  the 
growth  of  some  crops.  The  acidit}-  in  such  cases  may 
be  readily  corrected  by  the  use  of  lime  or  wood  ashes. 
Studies  conducted  by  the  Rhode  Island  Experiment 
Station  indicate  that  the  areas  of  acid  soils  are 
quite  extensive.  Acid  soils  can  be  distinguished  by 
their  action  upon  red  litmus  paper.  A  soil  may,  how- 
ever, give  an  acid  reaction  and  contain  a  fair  amount 
of  lime.  The  subject  of  acid  soils  and  liming  is  consid- 
ered in  Chapter  IX. 


ORGANIC    COMPOUNDS    OF   SOILS 


99 


io6.  Soils  in  Need  of  Humus.  —  Sandy  and  sandy 
loam  soils  that  have  been  cultivated  for  a  number  of 
years  to  corn,  potatoes,  and  small  grains,  without  the 
use  of  stable  manures  or  the  proper  rotation  of  crops, 
are  deficient  in  humus.  Clay  soils,  as  a  rule,  do  not 
stand  in  need  of  humus  so  much  as  loam  or  sandy 
soils.     The   mechanical  condition   of  heavv  clavs  is. 


Fig-.  20.  Humus  from  old  soil. 


H 


%Qx(/<gsn^'^^^- 


N 


\      Fis:.  21.  Humus  from  new  soil. 


however,  improved  by  the  addition  of  humus-forming 
material.  'x\lkali'  soils  are  usually  deficient  in  humus. 
Its  addition  to  loam  or  sandy  soils  is  beneficial  in  pre- 
venting the  soil  from  drifting  because  humus  binds 
together  the  soil  particles.  There  are  but  few  soils, 
under  ordinary  cultivation,  to  which  it  is  not  safe  to 
add  humus-forming  materials.  Ordinary  prairie  soils, 
for  the  first  ten  vears  after  breaking,  are  usually  well 


lOO  SOILS   AND    FERTII.IZERS 

supplied.  Swampy,  peaty,  and  muck  soils  contain 
large  amounts ;  in  fact,  they  are  often  overstocked 
with  humus. 

107.  Active  and  Inactive  Humus.  —  When  soil  has 
been  under  long  cultivation,  and  no  manures  have 
been  used,  the  nitrogen  and  mineral  matters  combined 
with  the  humus  are  reduced.  The  humus  from  long 
cultivated  fields  contains  a  higher  per  cent,  of  carbon 
than  that  from  well-manured  or  new  land ;  it  is  also 
less  active  because  of  the  higher  per  cent,  of  carbon 
which  does  not  readily  undergo  oxidation. '^ 

Humus  ironi  Humus  from 

new  soil.  old  soil. 

Per  ceut.  Per  cent. 

Carbon 44-12  50.10 

Hydrogen 6.00  4.80 

Oxygen 35.16  33.70 

Nitrogen 8.12  6.50 

Ash 6.60  4.90 

Total  humus  material  ••5.30  3.38 

108.  Influence  of  Different  Methods  of  Farming 
upon  Humus.  —  The  general  system  of  farming  has  a 
direct  effect  upon  the  humus  content  and  composition 
of  the  soil.  Where  live  stock  is  kept,  the  manure 
properly  used,  and  the  crops  systematically  rotated, 
the  crop-producing  power  of  the  land  is  not  decreased, 
as  in  the  case  of  the  one-crop  system.  The  influence 
of  different  systems  of  farming  upon  the  humus  con- 
tent and  other  properties  of  the  soil  ma)'  be  observed 
from  the  following  table  :^° 


ORGANIC    COMPOUNDS   OF    SOILS  lOl 

Phos- 
phoric 
acid  com-   Water- 
bined     holding 
Weight  Humus.  Nitrogen,    with        capac- 
per  cu.       Per  Per       humus.        ity. 

Character  of  soil.  ft.  lbs.      cent.         cent.    Per  cent.  Percent. 

,  Cultivated  thirty-five  years  ; 
rotation  of  crops  and  manure; 
high  state  of  productiveness.   70         3.32         0.30       0.04         48 

,  Originally  same  as  i  ;  con- 
tinuous grain  cropping  for 
thirty-five  years  ;  low  state  of 

productiveness 72         1.80        o.  16        o.oi  39 

Cultivated  forty-two  years  ; 
systematic  rotation  and  ma- 
nure ;  good  state  of  product- 
iveness        70         3.46         0.26        0.03         59 

Originally  same  as  3  ;  culti- 
vated thirty -five  years ;  no 
systematic  rotation  or  ma- 
nure ;  medium  state  of  pro- 
ductiveness     67         2.45         0.21        0.03         57 


CHAPTER  IV 


NITROGEN   OF  THE   SOIL   AND   AIR,    NITRIFICATION,  AND 
NITROGENOUS  MANURES 

109.  Importance  of  Nitrogen  as  a  Plant  Food. — 

The  illustration  (Fig.  22)  shows  an  oat  plant  which  has 
received  no  nitrogen,  while  potash,  phosphates,  lime,  and 
all  other  essential  elements  of  plant  food 
were  liberally  supplied.  Observ^e  the  pe- 
culiar and  restricted  growth,  with  but  little 
root  development.  The  leaves  w^ere  yel- 
lowish in  color. 

/^In  the  absence  of  nitrogen  a  plant 
makes  no  appreciable  growth.  With  only 
a  limited  supply,  a  plant  begins  its  growth 
in  a  normal  way  but  as  soon  as  the  avail- 
able nitrogen  is  used  up,  the  lower  and 
smaller  leaves  begin  gradually  to  die 
down  from  the  tips,  and  all  of  the  plant's 
energy  is  centered  in  one  or  two  leaves. 
In  one  experiment  when  only  a  small 
amount  of  nitrogen  was  supplied,  the  plant 
struggled  along  in  this  way  for  about  nine 
weeks,  making  a  total  growth  of  but  six 
and  one-half  inches.'^  Just  at  the  critical  point 
when  the  plant  was  dying  of  nitrogen  starvation, 
a  few  milligrams  of  calcium  nitrate  were  given.     In 


Fig.  22.   Oat 
plant  grown 
without  nitro- 
iren. 


NITROGEN    .AS    A    PLANT    FOOD  IO3 

thirty-six  hours  the  plant  showed  signs  of  renewed 
life,  the  leaves  assumed  a  deeper  green,  a  new  growth 
was  begun,  and  finally  four  seeds  were  produced. 
During  the  time  of  seed  formation  more  nitrogen  was 
added,  but  with  no  beneficial  result.  All  of  the 
essential  elements  for  plant  growth  were  liberally  pro- 
vided, except  nitrogen  which  was  very  sparingly  sup- 
plied at  first,  until  near  the  period  of  seed  formation, 
when  it  was  more  liberally  supplied. 

When  plants  have  reached  a  certain  period  in  their 
development,  and  have  been  starved  for  the  want  of 
nitrogen,  the  later  application  of  this  element  does  not 
produce  normal  growth,  as  the  energies  of  the  plant 
have  been  used  up  in  searching  for  food.  Nitrogen,  as 
well  as  potash,  lime,  and  phosphoric  acid,  are  all  neces- 
sary while  plants  are  in  their  first  stages  of  growth. 

In  the  case  of  wheat,  nitrogen  is  assimilated  more 
rapidly  than  are  any  of  the  mineral  elements.  Before 
the  plant  heads  out,  over  eighty-five  per  cent,  of  the 
total  nitrogen  required  has  been  taken  from  the  soil. 3^ 
Corn  also  takes  up  all  of  its  nitrogen  from  four  to  five 
weeks  before  the  crop  matures.  Flax  takes  up 
severity-five  per  cent,  of  its  nitrogen  during  the  first 
fifty  days  of  growth. 37 
n  Nitrogen  is  demanded  by  all  crops.  It  forms  the 
chief  building  material  for  the  proteids  of  all  plants. 
In  the  absence  of  a  sufficient  amount  of  nitrogen,  the 
rich  green  color  is  not  developed ;  the  foliage  is  of  a 
yellowish  tinge.     Nitrogen  is  one  of  the  constituents 


I04  SOILS    AND    FERTILIZERS 

of  chloroph}'!,  the  green  coloring-matter  of  plants, 
hence  with  a  lack  of  nitrogen  only  a  limited  amount 
of  chlorophyl  can  be  produced.  Plants  with  large, 
w^ell-developed  leaves  of  a  rich,  green  color  are  not 
suffering  for  nitrogen.  Nitrogenous  fertilizers  have 
a  tendency  to  produce  a  luxurious  growth  of  foliage 
deep  green  in  color.  . 

'    ATMOSPHERIC  NITROGEN  AS  A  SOURCE  OF   PLANT   FOOD 

110.  Early  Views.  —  In  addition  to  the  carbon,  hy- 
drogen, and  oxygen,  which  form  the  organic  com- 
pounds of  plants,  nitrogen  also,  at  the  beginning  of 
the  present  century,  was  known  to  be  present.  The 
sources  of  carbon,  h}'drogen,  and  oxygen,  for  crop 
purposes,  were  much  easier  to  determine  and  under- 
stand than  the  sources  of  nitrogen.  Priestley,  the  dis- 
coverer of  oxygen,  believed  that  the  free  nitrogen  of 
the  air  was  a  factor  in  supplying  plant  food.  De  Saus- 
sure  arrived  at  just  the  opposite  conclusion.  The  facts 
which  led  to  these  beliefs  were  not  convincing  because 
the  methods  of  chemical  analysis  had  not  yet  been 
sufficiently  perfected  to  solve  the  question. 3^ 

111.  Boussingault's  First  Experiments. — Boussin- 
gault  was  the  first  to  make  a  careful  study  of  the  sub- 
ject. In  a  prepared  soil,  free  from  nitrogen,  and  con- 
taining all  of  the  other  elements  necessary  for  plant 
growth,  he  grew  clover,  wheat,  and  peas,  carefully 
determining  the  nitrogen  in  the  seed.  The  plants 
were  allowed  free  access  to  the  air,  being  simply  pro- 


ATMOSPHERIC    NITROGEN 


^05 


tected  from  dust,  and  were  watered  with  distilled 
w^ater.  But  little  growth  was  made.  At  the  end  of 
two  months  the  plants  were  submitted  to  chemical 
analysis,  and  the  amount  of  nitrogen  present  was 
determined. 

His  first  results  are  mven  in  the  following  table  :39 


Nitrogen. 

In  seed  sown. 
Gram. 

Clover,  2  mos o.  1 1 


Wheat  2 


Peas       2     ' ' 

Boussineault 


In  plant. 
Gram. 

0.12 

0.156 

0.04 

0.06 

o.  10 


Gain. 
Gram. 


O.OI 

0.042 

^.003 

0.003 

0.053 

plants,    in 


a 


0.114 

0.043 

0.057 

0.047 

^  concluded    that    when 

sterile  soil,  were  exposed  to  the  air,  there  was  with 
some  a  slight  gain  of  nitrogen  but 
the  amount  gained  from  atmospheric 
sources  was  not  sufficient  to  feed  the 
plant  and  allow  it  to  reach  full  ma- 
turity. By  many  these  results  were 
not  accepted  as  conclusive. 

112.  Boussingault^s  Second  Ex- 
periments.—  Fifteen  years  later 
(1853)  Boussingault  repeated  his  ex- 
periments in  a  different  way.  The 
plants  were  grown  in  a  large  carboy 
with  a  limited  volume  of  air  so  as  to^ig-  23-  Plants  grown 

rr     11  p  .  in  carboy. 

cut  Oil  all  sources  of  combined  nitro- 

By  means  of  a  second  glass  vessel 


gen,  as  ammonia. 


I06  SOILS   AND    FERTILIZERS 

(^,  Fig.  23)  the  carboy  was  kept  supplied  with  a 
liberal  amount  of  carbon  dioxide,  so  that  plant  growth 
w^ould  not  be  checked  for  lack  of  this  material.  When 
experiments  were  carried  on  in  this  way  using  a  fertile 
soil,  the  plants  reached  full  maturity,  but  when  a  soil 
free  from  nitrogen  was  used,  plant  growth  was  soon 
checked.  A  general  summary  of  this  work  is  given  in 
the  following  table  :  ^9 

Nitrogen. 

In  seeds.  In  plant.  Loss. 

Gram.  Gram.  Gram. 

Dwarf  beans o.icxdi  0.0977  — 0.0024 

Oats 0.0109  0,0097  — 0.0012 

White  lupines 0.2710  0.2669  — 0.0041 

Garden  cress 0.0013  0.0013            

These  experiments  show  that  with  a  sterilized  soil, 
and  all  sources  of  combined  atmospheric  nitrogen  cut 
off,  the  free  nitrogen  of  the  air  takes  no  part  in  the 
food  supply  of  the  plant. 

113.  Boussingault's  Third  Experiments.  —  In  1854 
Boussingault  again  repeated  his  experiments;  this 
time  he  grew  the  plants  in  a  glass  case  so  constructed 
that  there  was  a  free  circulation  of  air  from  which  all 
combined  nitrogen  had  been  removed.  These  exper- 
iments were  similar  to  his  second  series ;  the  plants, 
however,  were  not  grown  in  a  limited  volume  of  air. 
The  results,  without  going  into  detail,  showed  that 
the  free  nitrogen  of  the  air,  under  the  conditions  of  the 
experiment,  took  no  part  in  the  food  supply  of  plants. 


ATMOSPHERIC    NITROGEN  IO7 

If  anything,  there  was  less  nitrogen  recovered  in  the 
dwarfed  plants  than  there  was  in  the  seed  sown. 

114.  Ville^s  Results. — About  the  same  time  Ville 
carried  on  a  series  of  experiments  of  like  nature,  but 
in  a  different  way,  and  arrived  at  just  the  opposite 
conclusions.  In  short,  his  experiments  indicated  that 
plants  w^ere  capable  of  making  liberal  use  of  the  free 
nitrogen  of  the  air  for  food  purposes.  The  directly 
opposite  conclusions  of  Boussingault  and  Ville,  led  to 
a  great  deal  of  controversy.  The  French  Academy  of 
Science  took  up  the  question,  and  appointed  a  commis- 
sion to  review  the  work  of  Ville.  The  commission 
consisted  of  six  prominent  scientists.  They  reported 
that  "M.  Ville's  conclusions  are  consistent  with  his 
labor  and  results."  ^^ 

115.  Work  of  Lawes  and  Gilbert.  —  Lawes  and 
Gilbert,  however,  carried  on  such  extensive  exper- 
iments under  a  variety  of  conditions  as  to  remove  all 
doubt  regarding  the  question.  Plants  were  grown  in 
sterilized  soils,  in  prepared  pumice  stone,  and  in  soils 
with  a  limited  and  known  quantity  of  nitrogen  beyond 
that  contained  in  the  seed.  Different  kinds  of  plants 
were  experimented  with.  The  w^ork  was  carried  on 
wnth  the  utmost  care  and  with  apparatus  so  constructed 
as  to  eliminate  all  controllable  factors.  The  results  in 
the  aggregate  clearly  indicate  that  plants,  when  acting  in 
a  sterile  medium,  are  unable  to  make  use  of  the  free  nitro- 
gen of  the  air  for  the  production  of  organic  matter.  ^^ 


I08  SOILS    AND    FERTILIZERS 

1 16.  Atwater's  Experiments.  —  Atwater  carried  on 
similar  experiments  in  this  country. 4°  Some  of  his 
results  indicate  that  when  seeds  germinate  they  lose  a  j 
small  part  of  their  nitrogen,  and  when  grown  in  a 
sterile  soil,  they  fail  to  fix  any  of  the  free  nitrogen  of 
the  air. 

In  all  of  the  work  of  the  different  investigators  prior 
to  1888,  plants  were  grown  in  a  sterilized  medium, 
and  under  these  conditions  they  are  unable  to  make 
use^  of  the  free  nitrogen  of  the  air. 

/*  117.  Field  and  Laboratory  Tests.  —  Experiments 
»  with  sterilized  soils  do  not  represent  the  normal 
conditions  of  growing  crops,  where  all  of  the 
bacteriological  agencies  of  the  soil,  the  air,  and  the 
plant,  are  free  to  act.  Experiments  have  shown  that 
these  agencies  have  an  important  bearing  upon  plant 
growth. 

In  a  five  years'  rotation  of  clover  and  other  legu- 
minous plants,  Lawes  and  Gilbert  found  that  a  soil 
gained  from  two  to  four  hundred  pounds  of  nitrogen 
in  addition  to  that  removed  in  the  crop,  while  land 
which  produced  wheat  continuously  had  gradually 
lost  nitrogen.  The  amount  in  the  subsoil  remained 
nearly  the  same.  All  of  these  facts  plainly  indicated 
that  crops  like  clover  have  the  power  of  gaining 
nitrogen  from  unknown  sources.  The  results  of 
prominent  German  agriculturists  led  to  the  same  con- 
clusion.    It  was  known  that  wheat  grown  after  clover 


ATMOSPHERIC    NITROGEN  IO9 

gave  as  good  results  as  the  use  of  nitrogenous  manure 
for  the  wheat,  but  for  many  years  this  fact  was  unex- 
plained. 

^^118.  HellriegePs  Experiments.  —  He  grew  legu- 
— Hiinous  plants  in  nitrogen-free  soils.  One  set  of  plants 
was  watered  with  distilled  water,  while  another  had  in 
addition  small  amounts  of  leachings  from  an  old  loam 
field.  The  plants  w^atered  with  distilled  water  alone 
made  but  little  growth,  while  those  watered  with  the 
loam  leachings  reached  full  maturity  and  contained 
something  like  a  hundred  times  more  nitrogen  than 
was  in  the  seed  sown.  The  dark  green  color  was  also 
developed,  showing  the  presence  of  a  normal  amount 
of  chlorophyl.  The  roots  of  the  plants  had  well- 
developed  swellings  or  nodules,  while  those  that  were 
watered  with  distilled  water  alone  had  none.  The 
loam  leachings  contained  only  a  trace  of  nitrogen.^' 

119.  Experiments  of  Wilfarth.  —  Experiments  by 
Wilfarth  give  more  exact  data  regarding  the  amount 
of  nitrogen  taken  from  the  air.  Lupines  were  grown 
in  the  same  way,  and  one  lot  watered  with  distilled 
water,  while  another  lot  received  in  addition  leachings 
from  an  old  lupine  field. 

Watered  with  distilled  water.  Watered  with  soil  leachings. 

Dry  matter.  Nitrogen.  Dry  matter.  Nitrogen. 

Grams.  Gram.  Grams.  Grams. 


0.919 

0.015 

44.72 

1.099 

0.800 

0.014 

45.61 

I.I53 

0.921 

0.013 

44.48 

1. 195 

1.021 

0.013 

42.45 

1-337 

no  SOILS    AND    FERTILIZERS  | 

These  experiments  have  been  verified  by  many 
other  investigators  until  the  fact  has  been  established 
that  leguminous  plants  may,  through  the  agency  of 
micro-organisms,  make  use  of  the  free  nitrogen  of  the 
air.  The  work  of  Hellriegel  was  not  accidental  but 
the  result  of  careful  and  systematic  investigation.  As 
early  as  1863  he  observed  that  clover  would  develop 
along  the  roadway  in  sand  in  which  there  was  scarcely 
a  trace  of  combined  nitrogen. 

120.  Composition  of  Root  Nodules.  —  The  root 
nodules  referred  to,  are  particularly  rich  in  nitrogen. 
In  one  experiment,  the  light-colored  and  active  ones 
contained  5.55  per  cent,  of  nitrogen  while  the  dark- 
colored  and  older  ones  contained  3.21  per  cent.  The 
entire  nodules  of  the  root  both  active  and  inactive 
contained  4.60  per  cent,  nitrogen.  The  root  itself 
contained  2.21  per  cent,  nitrogen.^^ 

The  root  nodules  also  contain  definite  and  charac- 
teristic micro-organisms,  and  it  was  the  spores  of  these 
*"  organisms  that  were  present  in  the  soil  extract  in  both 
HellriegePs  and  Wilfarth's  experiments.  In  the  ster- 
ilized soils  they  were  not  present.  These  organisms 
found  in  root  nodules,  are  the  essential  agents  which 
aid  in  the  fixation  of  the  free  nitrogen  of  the  air,  and 
^     in  its  ultimate  use  as  plant  food. 

121.  Nitrogen  in  the  Root  Nodules  Returned  to 
the  Soil.  —  Ward  has  shown  that  when  clover  roots 
decay,  the  organisms  and  nitrogen  present  in  the  nod- 


NITROGEN    COMPOUNDS    OF    THE    SOIL  III 

ules  are  distributed  within  the  soil. 3^  Hence  when- 
ever a  legnniinous  crop  is  raised,  nitrogen  is  added  to 
the  soil,  instead  of  being  taken  away,  as  in  the  case  of 
a  grain  crop.  The  amount  of  nitrogen  per  acre 
returned  to  the  soil  b}-  a  leguminous  crop  as  clover, 
varies  with  the  growth  of  the  crop.  In  the  roots  of  a 
clover  crop  a  year  old  there  are  present  from  20  to  30 
pounds  of  nitrogen  per  acre,  while  in  the  roots  and 
culms  of  a  dense  clover  sod,  two  or  three  years  old, 
there  may  be  present  75  pounds  or  more  of  nitrogen. 
Peas,  beans,  lucern,  cow  peas,  and  all  members  of  the 
leguminous  family  possess  the  powder  of  fixing  the  free 
nitrog-en  of  the  air  bv  means  of  micro-org-anisms. 
The  micro-organisms  associated  with  one  species  as 
clover  differ  from  these  associated  with  another  as 
lucern.  The  amount  of  nitrogen  which  the  various 
legumes  return  to  the  soil  is  variable.  Hellriegel's  re- 
sults are  of  the  greatest  importance  to  agriculture 
because  the}'  show  how  the  free  nitrogen  of  the  air  can 
be  utilized  indirectly  as  food,  by  crops  unable  to  appro^ 
priate  it  for  themselves. 

THE  NITROGEN  COMPOUNDS  OF  THE  SOIL 

122.  Origin  of  the  Soil  Nitrogen. — The  nitrogen  of 
the  soil  is  derived  chiefl}'  from  the  accumulated  re- 
mains of  animal  and  vegfetable  matter.  The  orio-inal 
source  of  the  soil  nitrogen,  that  is  the  nitrogen  which 
furnished  food  to  support  the  vegetation  from  which 
our  present  stock   of  soil  nitrogen  is    obtained,    was 


112  SOILS   AND    FERTILIZERS 

probably  the  free  nitrogen  of  the  air.  All  of  the 
ways  in  which  the  free  nitrogen  of  the  air  has  been 
made  available  to  plants  of  higher  orders  which  require 
combined  nitrogen,  are  not  known.  It  is  supposed, 
however,  that  this  has  been  brought  about  by  the 
workings  of  lower  forms  of  plant  life,  and  by  micro- 
organisms. Whatever  these  agencies  have  been  they 
do  not  appear  to  be  active  in  a  soil  under  high  cultiva- 
tion, because  the  tendency  of  ordinary  cropping  is  to 
reduce  the  supply  of  soil  nitrogen. 

123.  Organic  Nitrogen  of  the  Soil.  —  In  ordinary 
soils  the  nitrogen  is  present  mainly  in  organic 
forms  combined  with  the  carbon,  hydrogen,  and 
oxygen;  and  to  a  less  extent  with  the  mineral  ele- 
ments forming  nitrates.  The  organic  forms  of 
nitrogen,  it  is  generally  considered,  are  incapable  of 
supplying  plants  with  nitrogen  for  food  purposes  until 
the  process  known  as  nitrification  takes  place.  The 
nitrogenous  organic  compounds  in  cultivated  soils  are 
derived  mainly  from  the  undigested  protein  compounds 
of  manure  and  from  the  nitrogenous  compounds  in 
crop  residues.  When  decomposition  occurs,  amides, 
organic  salts,  and  other  allied  bodies  are  without 
doubt  produced  as  intermediate  products  before  nitrifi- 
cation takes  place.  The  organic  nitrogen  of  the  soil 
may  be  present  in  exceedingly  inert  forms  similar  to 
leather.  In  fact  in  many  peaty  soils  there  are  large 
amounts    of    inactive    organic    compounds    rich    in 


NITROGEN    COMPOUNDS   OF    THE    SOIL  II 3 

nitrogen.  In  other  soils  the  nitrogen  is  present  in 
less  complex  forms.  The  organic  nitrogen  of  the  soil 
may  vary  in  complexity  from  forms  like  the  nitrogen 
of  urea  to  forms  like  that  of  peat. 

124.  Amount  of  Nitrogen  in  Soils.  —  The  fertility 
of  any  soil  is  dependent,  to  a  great  extent,  upon  the 
amount  and  form  of  its  nitrogen.  In  soils  of  the 
highest  degree  of  fertility  there  is  usually  present 
from  0.2  to  0.3  per  cent,  of  total  nitrogen,  equivalent 
to  from  7,000  to  10,000  pounds  per  acre  to  the  depth 
of  one  foot.  j\Iany  soils  of  good  crop-producing 
power  contain  as  low  as  0.12  per  cent,  of  nitrogen. 
There  is  usually  two  or  three  times  more  nitrogen  in 
the  surface  soil  than  in  the  subsoil.  In  many  sandy 
soils  which  have  been  allow^ed  to  decline  in  fertility 
the  nitrogen  may  be  less  than  0.04  per  cent.  Of  the 
total  nitrogen  in  soils  there  is  rarely  more  than  2  per 
cent,  at  any  one  time,  in  forms  available  as  plant 
food.43  A  soil  with  5,000  pounds  of  total  nitrogen 
per  acre  would  contain  about  100  pounds  of  available 
nitrogen  of  which  only  a  part  comes  in  contact  w4th 
the  roots  of  crops.  Hence  it  is  that  a  soil  may  con- 
tain a  large  amount  of  total  nitrogen  and  yet  be  defi- 
cient in  available  nitrogen. 

125.  Amount  of  Nitrogen  Removed  in  Crops. 
—  The  amount  of  nitrogen  removed  in  crops  ranges 
from  25  to  100  pounds  per  acre  depending  upon  the 
nature  of  the  crop.     It  does  not  necessarily  follow  that 


114  SOILS   AND    FERTILIZERS 

the  crop  which  removes  the  largest  amount  of  nitrogen 
leaves  the  land  in  the  most  impoverished  condition. 
Wheat  and  many  grains,  while  they  do  not  remove 
such  a  large  amount  of  nitrogen  in  the  crop,  leave 
the  soil  more  exhaused  than  if  other  crops  were  grown. 
This,  as  will  be  explained,  is  caused  by  the  loss  of 
nitrogen  from  the  soil  in  other  ways  than  through  the 
crop.37 

Pounds  of  nitrogen 
per  acre. 

Wheat,  20  bushels 25 

Straw,  2000  pounds 10 

Total '....   35 

Barley,  40  bushels 28 

Straw,  3000  pounds 12 

Total 40 

Oats,  50  bushels 35 

Straw,  3000  pounds i 15 

Total 50 

Flax,  15  bushels 39 

Straw,  1800  pounds 15 

Total 54 

Potatoes,  150  bushels 40 

Corn,  65  bushels 40 

Stalks,  3000  pounds 35 

Total 75 

126.  Nitrates  and  Nitrites. — The  amount  of  nitro- 
gen in  the  form  of  nitrates  and  nitrites,  varies  from 
mere  traces  to  150  pounds  per  acre.     Calcium  nitrate 


NITROGEN    COMPOUNDS    OF    THE    SOIL  II5 

is  the  usual  form  met  with,  especially  in  soils  which 
are  sufficiently  supplied  with  calcium  carbonate  to 
allow  nitrification  to  progress  rapidly.  Nitrates  and 
nitrites  are  the  most  valuable  forms  of  nitrogen  for 
plant  food.  Both  are  produced  from  the  organic 
nitrogen  of  the  soil.  A  nitrate  is  a  compound  com- 
posed of  a  base  element  as  sodium,  potassium,  or 
calcium,  combined  with  nitrogen  and  oxygen.  A 
nitrite  contains  less  oxygen  than  a  nitrate. 

Potassium  nitrate,  KNO  ,  sodium  nitrate,  NaNO  , 
and  calcium  nitrate,  Ca(NO  )^,  are  the  nitrates  which 
are  of  most  importance  in  agriculture.  The  nitrites, 
as  potassium  nitrite,  KNO^,  are  met  with  to  a  less 
extent  than  the  nitrates.  Nitrates  and  nitrites  are 
present  in  surface  well  waters  contaminated  with 
animal  and  vegetable  matter.  IMany  well  waters 
possess  some  material  value  as  a  fertilizer  on  account 
of  the  nitrates,  nitrites,  and  decaying  animal  and 
vegetable  matters  which  they  contain. 

127.  Ammonium  Compounds  of  the  Soil.  —  The 
amount  of  ammonium  compounds  in  a  soil  is  usually 
less  than  the  amount  of  nitrates  and  nitrites.  The 
sources  of  the  ammonium  compounds  are :  rain-water 
and  the  ammonia  formed  from  the  decay  of  the 
organic  matter.  Like  the  nitrates  and  nitrites,  the 
ammonium  compounds  are  all  soluble  and  hence  can- 
not accumulate  in  soils  which  receive  an  average 
amount  of  rainfall.      Thev  are  usuallv  found  in  all 


Il6  SOILS   AND    FERTILIZERS 

surface  well  waters.  In  the  soil,  the  ammonium  com- 
pounds may  be  oxidized  and  form  nitrates.  Com- 
pounds as  ammonium  chloride  or  ammonium  carbonate, 
if  present  in  a  soil  in  excessive  amounts,  will  destroy 
vegetation  in  a  w^ay  similar  to  the  alkaline  compounds 
in  alkaline  soils. 

128.  Nitrogen  in  Rain-water  and  Snow.  —  The 
amount  of  nitrogen  w^hich  is  annually  returned  to  the 
soil  in  the  form  of  ammonium  compoimds  dissolved  in 
rain-w^ater  and  snow,  is  equivalent  to  from  2  to  3 
pounds  per  acre.  At  the  Rothamsted  experiment 
station  the  average  amount  for  eight  years  was  2)- 2)7 
pounds.43  When  a  soil  is  rich  in  nitrogen  the  gain 
from  rain  and  snow  is  only  a  partial  restoration  of  that 
wdiich  has  been  given  off  from  the  soil  to  the  air  or 
lost  in  the  drain  waters.  The  principal  form  of  the 
nitrogen  in  rain  water  is  ammonium  carbonate  which 
is  present  in  the  air  to  the  extent  of  about  22  parts  per 
million  parts  of  air. 

129.  Ratio  of  Nitrogen  to  Carbon  in  the  Organic 
Matter  of  Soils. — In  some  soils  the  organic  matter  is 
more  nitrogenous  than  in  others.  In  those  of  the 
arid  regions  the  humus  contains  from  15  to  20  per 
cent,  of  nitrogen,  while  soils  from  the  humid  regions 
contain  4  to  6  per  cent.^^  In  some  soils  the  ratio  of 
nitrogen  to  carbon  may  be  i  to  6,  while  in  others  it 
may  be  i  to  18  or  more.  That  is,  in  some  soils  there 
is  I   part  of  nitrogen   to  6  parts  of  carbon,    while   in 


NITROGEN    COMPOUNDS   OF   THE    SOIL  II 7 

others  the  organic  matter  contains  i  part  of  nitrogen 
to  18  parts  of  carbon.  In  a  soil  where  there  exists  a 
wide  ratio  between  the  nitrogen  and  carbon,  it  is 
believed  that  the  conditions  for  supplying  crops  with 
available  nitrogen  are  unfavorable. 

130.  Losses  of  Nitrogen  from  Soils.  —  When  a  soil 
rich  in  nitrogen  is  cultivated  for  a  number  of  years 
exclusively  to  grain  crops  there  is  a  loss  of  nitrogen 
exceeding  the  amount  removed  in  the  crop,  caused  by 
the  rapid  oxidation  of  the  organic  matter  of  the  soil. 
Experiments  have  shown  that  when  a  soil  of  average 
fertility  is  cultivated  continually  to  grain  that  for 
every  25  pounds  of  nitrogen  removed  in  the  crop  there 
is  a  loss  of  146  pounds  from  the  soil  due  to  the 
destruction  of  the  organic  matter. '^  In  general,  any 
system  of  cropping  which  keeps  the  soil  continually 
under  the  plow,  results  in  decreasing  the  nitrogen. 
When  a  soil  is  rich  in  nitrogfen  the  grreatest  losses 
occur;  when  poor  in  nitrogen  there  is  relatively  less 
loss.  There  is  a  tendency  toward  the  establishment 
of  an  equilibrium  as  to  the  nitrogen  content  of  soils. 
When  a  soil  rich  in  nitroofen  is  g-iven  arable  culture 
the  oxidation  of  the  organic  matter  and  the  losses  of 
nitrogen  take  place  rapidly. 

131.  Gain  of  Nitrogen  in  Soils. — When  arable 
land  is  permanently  covered  with  vegetation,  there  is 
a  gain  of  nitrogen.  Pasture  land  contains  more  nitro- 
gen than  cultivated  land  of  a  similar  character ;  also 


Il8  SOILS    AND    FERTILIZERS 

ill  meadow  land  there  is  a  tendency  for  the  nitrogen 
to  increase.  These  facts  are  well  illnstrated  in  the 
investigations  of  Lavves  and  Gilbert,  at  Rothamsted.^3 

Age  of  pasture.  Nitrogen. 

Years.  Per  cent. 

Arable  land o.  14 

Barn-field  pasture 8  o.  151 

Apple-tree  pasture 18  o.  174 

Meadow 21  o.  204 

Meadow 30  0.241 

After  dednctino;  the  amount  of  nitrog^en  in  the  manure 
added  to  the  meadow  land,  the  annual  gain  of  nitrogen 
was  more  than  44  pounds  per  acre. 

Another  source  of  gain  of  nitrogen  is  the  fixation  of 
the  free  nitrogen  of  the  air  by  the  growth  of  clover 
and  other  leguminous  crops.  ■  If  a  soil  is  properly 
manured  and  cropped  the  amount  of  nitrogen  may  be 
increased.  A  rotation  of  wheat,  clover,  wheat,  oats,  and 
corn  with  manure  will  leave  the  soil  at  the  end  of  the 
period  of  rotation  in  better  condition  as  regards  nitro- 
gen than  at  the  beginning.  These  facts  are  illustrated 
in  the  following  table  :'7 

Continuous  wheat  culture — 

Nitrogen  in  soil  at  beginning  of  experiment 0.221  per  cent. 

Nitrogen  at  end  of  5  years  continuous  wheat  cultiva- 
tion   0.193    "       " 

Loss  per  annum  per  acre  (in  crop  24.5,  soil  146.5) . .  171  pounds. 

Rotation  of  crops — 

Nitrogen  in  soil  at  beginning  of  rotation 0.221  per  cent. 

Nitrogen  at  close  of  rotation 0.231    "        " 

Gain  to  soil  per  annum  per  acre 61  pounds. 

Nitrogen  removed  in  crops  per  annum 44       " 


NITRIFICATION  II9 

It  is  to  be  reg^retted  that  in  the  cultivation  of  largfe 
areas  of  land  to  staple  crops  as  wheat,  corn,  and  cotton, 
the  methods  of  cultivation  are  such  as  to  decrease  the 
nitrogen  content  and  crop-producing  power  of  the  soil 
when  this  can  be  prevented. 

NITRIFICATION 

132.  Former    Views    Regarding    Nitrification. — 

The  presence  of  nitrates  and  nitrites  in  soils  was 
formerly  accounted  for  by  oxidation.  The  theory 
was  held  that  the  production  of  nascent  nitrogen  by 
the  decomposition  of  organic  matter  caused  a  union 
between  the  oxvg-en  of  the  air  and  the  nitroo-en  of  the 
organic  matter.  The  studies  of  fermentation  by 
Pasteur  led  him  to  believe  that  possibly  the  formation 
of  nitric  acid  in  the  soil  might  be  due  to  fermentation. 
It  was,  however,  15  years  later  before  the  French 
chemists,  Schlosing  and  ^Miintz,  established  the  fact 
that  nitrification  is  produced  by  a  living  organism. 

133.  Nitrification    Caused    by     Micro-organisms. 

—  Nitrification  is  the  process  by  which  nitrates 
or  nitrites  are  produced  in  soils,  by  the  workings  of 
org^anisms.  Nitrification  results  in  chanmno^  the  com- 
plex  organic  nitrogen  of  the  soil  to  the  form  of  nitrates 
or  nitrites.  It  is  the  process  by  which  the  inert 
nitrogen  of  the  soil  is  rendered  available  as  crop  food. 
The  organisms  which  carry  on  the  work  of  nitrifica- 
tion have  been  isolated  and  studied  by  Warington, 
and  by  Winogradsky. 


I20  SOILS   AND    FERTILIZERS 

134.  Conditions   Necessary  for   Nitrification  are : 

1.  Food  for  the  nitrifying  organisms. 

2.  A  supply  of  ox\'gen. 

3.  Moisture. 

4.  A  favorable  temperature. 

5.  Absence  of  strong  sunlight. 

6.  The  presence  of  some  basic  compound. 

In  order  to  allow  nitrification  to  proceed,  all  of  these 
conditions  must  be  satisfied.  The  process  is  fre- 
quently checked  because  some  of  the  conditions,  as 
presence  of  a  basic  compound,  are  unfulfilled. 

135.  Food   for   the    Nitrifying    Organisms. — All 

living  organisms  require  a  supply  of  food  and  one  of 
the  food  requirements  of  the  nitrifying  organism  is  a 
supply  of  phosphates.  In  the  absence  of  phosphoric 
acid,  nitrification  cannot  take  place.  The  change 
which  the  phosphoric  acid  undergoes  in  serving  as 
food  for  the  nitrif}'ing  organism  is  unknown,  but  it 
doubtless  makes  the  phosphoric  acid  more  available  as 
plant  food.  The  principal  organic  food  of  the  nitrify- 
ing organism  is  the  organic  matter  of  the  soil. 
Organic  matter,  only  when  incorporated  with  soil,  can 
serve  as  food  for  the  nitrifying  organism.  In  the  pres- 
ence of  a  large  amount  of  organic  matter,  as  in  a 
manure  pile,  nitrification  does  not  take  place.  The 
process  can  take  place  only  when  the  organic  matter 
is  largely   diluted   with  soil.     Under  favorable  condi- 


FiQ.  I  •    Nitric  Organism  in  Potassium  Nitrite  Solution. 


^       «i-: 


\y 


fe      - 


A         ! 


%    IT 


-? 


Fig.  2.    Bacillus  reducing  Nitrates  to  free  Nitrogen  Gas. 
PLATE  I. 


NITRIFICATION  12  1 

tions  nitrifying  organisms  may  take  all  of  their  food 
as  inorganic  forms ;  that  is,  nitrification  may  take 
place  in  the  absence  of  organic  matter  provided  the 
proper  mineral  food  be  snpplied.  When  growth 
under  such  conditions  takes  place  the  organisms  assim- 
ilate carbon  from  the  combined  carbon  of  the  air,  and 
produce  organic  carbon  compounds.  That  is,  an 
organism,  working  in  the  absence  of  sunlight  and  un- 
provided with  chlorophyl,  ma}'  construct  organic  car- 
bon compounds/3  The  nitrification  which  takes  place  in 
the  absence  of  nitrogenous  organic  matter  is  of  too 
limited  a  character  to  supply  growing  crops  with  all 
of  their  available  nitrogen.  For  general  crop  produc- 
tion the  organic  matter  of  the  soil  is  the  source  of  the 
nitrogen  which  undergoes  the  nitrification  process, 
and  which  furnishes  food  for  the  nitrifying  organisms. 

136.  Oxygen  Necessary  for  Nitrification.  —  The 
second  requirement  for  nitrification  is  an  adequate 
supply  of  oxygen.  The  nitrification  organism  belongs 
to  that  class  of  ferments  (aerobic)  which  requires  oxy- 
gen for  existence.  Oxygen  is  present  as  one  of  the  ele- 
ments in  the  final  product  of  nitrification  as  in  calcium 
nitrate,  Ca(NO  )^.  In  the  absence  of  oxygen  the  nitri- 
fication process  is  checked.  When  soils  are  saturated 
with  water,  the  process  cannot  go  on  for  want  of  ox}'gen. 
In  well-cultivated  soils,  particularly  clay  soils,  the  con- 
ditions for  nitrification  are  improved  b}'  aeration  be- 
cause the  supply  of  oxygen  in  the  soil  spaces  is  increased. 


122  SOILS    AND    FERTILIZERS 

137.  Moisture  Necessary  for  Nitrification.  —  Nitri- 
fication cannot  take  place  in  a  soil  deprived  of  mois- 
ture. As  in  all  fermentation  processes,  so  with  nitri- 
fication, moistnre  is  necessary  for  the  chemical  changes 
to  take  place.  In  a  very  dry  time  nitrification  is 
arrested  for  the  want  of  water.  Water  is  as  necessary 
for  the  growth  and  development  of  the  living  organism 
which  carries  on  the  work  of  nitrification,  as  it  is  to 
the  life  of  a  plant  of  higher  order. 

138.  Temperatures  Favorable  for  Nitrification. — 

The  most  favorable  temperatures  for  nitrification  are 
between  12°  C.  (54°  F.)  and  i^f  C.  (99°  F.).  It  may 
take  place  at  as  low  a  temperature  as  3°  or  4°  C. 
(37°  and  39°  F.);  at  50°  C.  (122°  F.)  it  is  feeble, 
while  at  55°  C.  (130°  F.)  there  is  no  action.  ^^^  in 
northern  latitudes  nitrification  is  checked  during  the 
winter,  while  in  southern  latitudes  this  change  takes 
place  during  the  entire  year.  Crops  which  re- 
quire their  nitrogen  early  in  the  growing  season  are 
frequently  placed  at  a  disadvantage  because  there  is  less 
available  nitrogen  in  the  soil  at  that  time  than  later. 

139.  Strong  Sunlight  Checks  Nitrification. — Nitri- 
fication cannot  take  place  in  strong  sunlight;  it  pre- 
vents the  action  of  all  organisms  of  this  class.  In 
fallow  land  there  is  no  nitrification  at  the  surface  but 
immediately  below  where  the  surface  soil  excludes  the 
sunlight,  it  is  most  active.  In  a  cornfield  it  is  more 
active  than  in  a  compacted  fallow  field. 


NITRIFICATION  I23 

140.  Base-forming  Elements  Essential  for  Nitrifi- 
cation. —  The  presence  of  some  base-forming  element  to 
combine  with  the  nitric  acid  prodnced  is  a  necessary 
condition  for  nitrification,  and  for  this  pnrpose  calcium 
carbonate  is  particularly  valuable.  The  absence  of 
basic  materials  is  one  of  the  frequent  causes  of  non- 
nitrification.  In  acid  soils,  the  process  is  checked  for 
the  want  of  proper  basic  material.  The  organisms 
which  carry  on  the  work  cannot  exist  in  a  strong  acid 
or  alkaline  solution,  consequently  in  strong  acid  or 
alkaline  soils  the  ordinary  process  cannot  take  place. '^ 

141.  Nitrous  Acid  Organisms.  —  There  are  at  least 
two  nitrifying  organisms  in  the  soil :  one  produces 
nitrates  and  the  other  nitrites  or  nitrous  acid.  It  is 
believed  that  the  process  takes  place  in  two  stages,  the 
first  being  performed  by  the  nitrous  organism,  and  the 
process  completed  b}'  the  nitric  organism.  Warington 
says  that  "both  organisms  are  present  in  the  soil  in 
enormous  numbers, — and  the  action  of  the  two  organ- 
isms proceeds  together,  as  the  conditions  are  favorable 
to  both." 

142.  Ammonia-producing  Organisms.  —  There  are 
also  present  in  the  soil  organisms  which  have  the 
power  of  producing  ammonia  from  proteid  bodies. 
The  ammonium  compounds  produced  are  acted  upon 
by  the  nitrifying  organisms  and  readily  undergo 
nitrification.  "^^ 

143.  Denitrification  is  just  the  reverse  of  the  nitri- 


124  SOILS   AND    FERTILIZERS 

fication  process,  and  is  the  result  of  the  workings  of  a 
class  of  organisms  which  feed  upon  the  nitrates  form- 
ing free  nitrogen  which  is  liberated  as  a  gas.  One  of 
the  conditions  for  denitrification  is  absence  of  air,  as 
the  organism  belongs  to  the  anaerobic  class.  Denitri- 
fication readily  takes  place  in  soils  saturated  with 
water,  and  wdiere  the  soil  is  compacted  so  that  air  is 
practically  excluded.  ^^ 

144.  Number  and  Kinds  of  Organisms  in  Soils. — 
In  addition  to  the  micro-organisms  which  carry  on  the 
work  of  nitrification,  denitrification,  and  ammonifica- 
tion,  there  are  a  great  many  others,  some  of  which  are 
beneficial  while  others  are  injurious  to  crop  growth. 
It  has  been  estimated  that  in  a  gram  of  an  average 
sample  of  soil  there  are  from  60,000  to  500,000  bene- 
ficial and  injurious  micro-organisms.  ^^  There  are  pro- 
duced from  many  crop  residues,  by  injurious  ferments, 
chemical  products  w^hich  may  be  destructive  to  crop 
growth.  Flax  straw  for  example  when  it  decays  in 
the  soil  forms  products  which  are  destructive  to  a  suc- 
ceeding flax  crop. 

A  moist  soil,  rich  in  organic  matter,  and  containing 
various  salts,  may  form  the  medium  for  the  propaga- 
tion of  all  classes  of  organisms.  Sewage-sick  soils, 
clover-sick  soils,  and  flax-diseased  lands  are  all  the  re- 
sults of  bacterial  diseases.  Many  of  the  organisms 
which  are  the  cause  of  such  diseases  as  typhoid  fever, 
cholera,  and  diphtheria,  may   propagate  and  develop 


NITRIFICATION  I25 

in  a  moist  soil  under  certain  conditions,  and  then  find 
their  way  through  drain  waters  into  surface  wells,  and 
cause  the  spreading  of  these  diseases. 

145.  Products  Formed  by  Soil  Organisms.  —  In 
considering  the  part  which  micro-organisms  take  in 
plant  growth,  as  well  as  in  all  similar  processes,  there 
are  tw^o  phases  to  be  considered :  (i)  the  action  of  the  or- 
ganism itself,  and  (2)  the  chemical  action  of  the  product 
of  the  organism.  In  the  case  of  nitrification,  the 
action  of  the  organism  brings  about  a  change  in  the 
composition  of  the  organic  matter,  producing  nitric 
acid  which  is  merely  a  product  formed  as  a  result  of 
the  action  of  the  organism.  The  nitric  acid  then  acts 
upon  the  soil  producing  nitrates.  In  the  case  of  soils 
rich  in  organic  matter,  the  fermentation  changes 
which  take  place  during  humification  result  in  the 
production  of  acid  products.  This  is  simply  the 
result  of  the  action  of  the  ferments.  The  acids  then 
act  upon  the  soil  bases  and  produce  humates  or  organic 
salts.  In  many  fermentation  changes  there  is  first 
the  production  of  some  chemical  compound,  and  then 
the  action  of  this  compound  upon  other  bodies.  In 
rendering  plant  food  available,  as  in  nitrification  and 
humification,  it  is  the  final  product,  and  not  the  first 
product  of  the  organism,  which  is  of  value. 

146.  Inocculating  Soils  with  Organisms .  —  In  grow- 
ing leguminous  crops  on  soils  where  they  have  never 
before  been  produced,  it  has  been  proposed  to  supply 


126  SOILS   AND    FERTILIZERS 

the  essential  organisms  which  assist  the  crops  to 
obtain  their  nitrogen.  For  example,  if  clover  is 
grown  on  new  land,  the  soil  is  liable  to  be  deficient  in 
the  organisms  which  assist  in  the  assimilation  of 
nitrogen  and  which  are  present  in  the  root  nodules  of 
the  plant.  If  these  organisms  are  supplied,  better 
conditions  for  growth  exist.  The  extent  to  which  it 
is  necessary  to  inoculate  soils  with  organisms  for  the 
assimilation  of  nitrogen,  has  not  yet  been  determined 
by  actual  field  experiments. 

147.  Loss  of  Nitrogen  by  Fallowing  Rich  Lands. 
—  Summer  fallowing  creates  conditions  favorable  to 
nitrification.  A  fallow  is  beneficial  to  a  succeeding 
crop  because  of  the  nitrogen  which  is  rendered  a^'ail- 
able.  If  a  soil  is  rich  in  nitrogen  and  lime,  summer 
fallowing  causes  the  production  of  more  nitrates  than 
can  be  retained  in  the  soil.  The  crop  utilizes  only  a 
part  of  the  nitrogen  rendered  available,  the  rest  being 
lost  by  drainage,  ammonification,  and  denitrification. 
Hence  the  available  nitrogen  is  increased  while  the 
total  nitrogen  is  greatly  decreased.  '^ 

Soil  before  Soil  after 

fallowing.  fallowing. 

Total  nitrogen o.  154  o.  1 42 

Soluble  nitrogen 0.002  0.004 

The  gain  of  0.002  per  cent,  of  soluble  nitrogen  was 
accompanied  by  a  loss  of  0.012  per  cent,  of  total 
nitrogen.  For  every  pound  of  available  nitrogen 
there  was  a  loss  of  6  pounds. 


NITRIFICATION  1 27 

148.  Deep  and  Shallow  Plowing  and  Nitrification. 

—  In  a  rich  prairie  soil  nitrification  goes  on  very 
rapidly.  This  is  one  reason  why  shallow  plowing  on 
new  breaking  gives  better  results  than  deep  plowing. 
Deep  plowing  at  first  causes  nitrification  to  take  place 
to  such  an  extent  that  the  crop  is  overstimulated  in 
growth.  Deep  plowing  and  thorough  cultivation  aid 
nitrification.  The  longer  a  soil  has  been  cultivated, 
the  deeper  and  more  thorough  must  be  the  cultivation. 

149.  Spring  and  Fall  Plowing,  and  Nitrification. 

—  Early  fall  plowing  leaves  more  available  nitrogen 
at  the  disposal  of  the  crop  than  late  fall  plowing. 
Nitrification  takes  place  only  near  the  surface.  Hence 
when  late  spring  plowing  is  practiced  there  is  brought 
to  the  surface  raw^  nitrogen,  while  the  available 
nitrogen  has  been  plowed  under,  and  is  beyond  the 
reach  of  the  young  plants  when  they  require  the  most 
help  in  obtaining  food.  The  various  methods  of 
cultivation  as  deep  and  shallow  plowing,  spring 
and  fall  plowing,  and  surface  cultivation  have  as  much 
influence  upon  the  available  nitrogen  supply  of  crops 
as  upon  the  water  supply.  The  saying  that  cultiva- 
tion makes  plant  food  available  is  parti cularh'  true  of 
the  element  nitrogen,  the  supply  of  which  is  capable 
of  being  increased  or  decreased  to  a  greater  extent 
than  that  of  an)-  other  element. 


NITROGENOUS  MANURES 

150.  Sources     of     Nitrogenous     Manures.  —  The 

materials  used  for  enriching  soils  with  nitrogen,  to 
promote  crop  growth,  may  be  divided  into  three 
classes:  (i)  organic  nitrogenous  manures,  (2)  nitrates, 
and  (3)  ammonium  salts.  Each  of  these  classes  has  a 
different  value  as  plant  food.  In  fact  there  are 
marked  differences  in  fertilizer  value  between  mate- 
rials belonging  to  the  same  class.  The  nitrogenous 
organic  materials  used  for  fertilizing  purposes  are  : 
dried  blood,  tankage,  meat  scraps  and  flesh  meal,  fish 
offal,  cottonseed  meal,  and  leguminous  crops  as  clover 
and  peas.  The  nitrogen  in  these  substances  is  princi- 
pally in  the  form  of  protein.  When  peat  and  muck 
are  properly  used  they  may  also  be  classed  among  the 
nitrogenous  manures. 

151.  Dried  Blood.  —  This  is  obtained  by  drying  the 
blood  and  debris  from  slaughter-houses.  Frequently 
small  amounts  of  salt  and  slaked  lime  are  mixed  with 
the  blood.  It  is  richest  in  nitrogen  of  any  of  the 
organic  manures.  When  thoroughly  dry  it  may  con- 
tain 14  per  cent,  of  nitrogen.  As  usually  sold,  it  con- 
tains from  10  to  20  per  cent,  of  water,  and  has  a 
nitrogen  content  of  from  9  to  13.  Dried  blood 
contains  only  small  amounts  of  other  fertilizer  ele- 
ments. It  is  strictly  a  nitrogenous  fertilizer,  readily 
yielding    to    the  action    of    micro-organisms    and    to 


NITROGENOUS   MANURES  1 29 

nitrification  ;  on  acconnt  of  its  fermentable  nature,  it 
is  a  quick-acting  fertilizer,  and  is  one  of  the  most 
valuable  of  the  organic  materials  used  as  manure. 
Dried  blood  may  be  applied  as  a  top  dressing  on  grass 
land.  It  gives  the  best  returns  when  used  on  an 
impoverished  soil  to  aid  crops  in  the  early  stages  of 
growth,  before  the  inert  nitrogen  of  the  soil  becomes 
available.  It  is  also  an  excellent  form  of  fertil- 
izer to  use  on  many  garden  crops,  but  it  should  not  be 
placed  in  direct  contact  w4th  seeds,  as  it  will  cause 
rotting,  nor  should  it  be  used  in  too  large  amounts. 
Three  hundred  pounds  per  acre  is  as  much  as  should 
be  applied  at  one  time.  When  too  much  is  used  losses 
of  nitrogen  may  occur  by  leaching  and  by  denitrifica- 
tion.  It  is  best  applied  directly  to  the  soil,  as  a  top 
dressing  in  the  case  of  grass,  or  near  the  seeds  of 
garden  crops,  and  not  mixed  wnth  unslaked  lime  or 
wood  ashes,  but  each  should  be  used  separately.  As 
all  plants  take  up  their  nitrogen  early  in  their  growth, 
nitrogenous  fertilizers  as  blood  should  be  applied  be- 
fore seeding  or  soon  after.  An  application  of  dried 
blood  to  partially  matured  garden  crops  will  cause  a 
prolonged  growth  and  very  late  maturity. 

Storer  gives  the  following  directions  for  preserving 
any  dried  blood  produced  upon  farms. ^'  "  The  blood 
is  thoroughly  mixed  in  a  shallow  box  with  4  or  5 
times  its  weight  of  slaked  lime.  The  mixture  is  cov- 
ered with  a  thin  laver  of  lime  and  left  to  drv  out.     It 


130  SOILS   AND    FERTILIZERS 

will  keep  if  stored  in  a  cool  place,  and  may  be  applied 
directly  to  the  land  or  added  to  a  compost  heap." 

The  price  per  pound  of  nitrogen  in  the  form  of 
dried  blood  can  be  determined  from  the  cost  and  the 
analysis  of  the  material.  A  sample  containing  9  per 
cent,  of  nitrogen  and  selling  for  $20  per  ton  is  equiva- 
lent to  1 1. 1 1  cents  per  pound  for  the  nitrogen  (2000  X 
0.09  =  180.     $20.00  ^-  180  =  II. II  cents). 

152.  Tankage  is  composed  of  miscellaneous  refuse 
matter  as  bones,  trimmings  of  hides,  hair,  horns,  hoofs, 
and  some  blood.  The  fat  and  gelatin  are,  as  a  rule, 
first  removed  b}'  subjecting  the  material  to  superheated 
steam.  This  miscellaneous  refuse,  after  drying,  is 
ground  and  sometimes  mixed  with  a  little  slaked  lime 
to  prevent  rapid  fermentation. 

Tankage  contains  less  nitrogen  but  more  phosphoric 
acid  than  dried  blood.  Owing^  to  its  miscellaneous 
nature,  it  is  quite  variable  in  composition,  as  the  fol- 
lowing analyses  of  tankage  from  the  same  abattoir  at 
different  times  show.'^ 

First  year.  Second  j'ear.  Third  year. 

Moisture 10.5  9.8  10.9 

Nitrogen 5.7  7.6  6.4 

Phosphoric  acid 12.2  10.6  11.7 

As  a  general  rule,  tankage  contains  from  5  to  8  per 
cent,  of  nitrogen  and  from  6  to  14  per  cent,  of  phos- 
phoric acid.  It  is  much  slower  in  its  action  than 
dried  blood,  and  supplies  the  crop  with  both  nitrogen 
and  phosphoric  acid.     Tankage  is  a  valuable  form  of 


NITROGENOUS    MANURES  13I 

fertilizer  to  use  for  garden  purposes.  It  may  also  be 
used  as  a  top  dressing  on  grass  lands,  and  may  be 
spread  broadcast  on  grain  lands.  It  is  best  to  apply 
the  tankage,  when  possible,  a  few  days  prior  to  seed- 
ing, and  it  should  not  come  in  contact  with  seeds. 
Two  hundred  and  fifty  pounds  per  acre  is  a  safe  dress- 
ing, and  when  there  is  sufficient  rain  to  ferment  the 
tankage,  400  pounds  per  acre  may  be  used.  A  dressing 
of  800  pounds  in  a  dry  season  would  be  destructive  to 
vegetation.  On  impoverished  soil  more  may  be  used 
than  on  soils  which  are  for  various  reasons  out  of 
condition.  The  cost  of  the  nitrogen,  as  tankage,  may 
be  determined  from  the  composition  and  selling  price. 
If  tankage  containing  7  per  cent,  of  nitrogen  and  12 
per  cent,  of  phosphoric  acid  is  selling  for  $22  per  ton, 
what  is  the  cost  of  the  nitrogen  per  pound  ?  The 
market  value  of  phosphoric  acid,  in  the  form  of  bones, 
should  first  be  ascertained.  Suppose  that  bone  phos- 
phoric acid  is  selling  for  4  cents  per  pound.  The 
phosphoric  acid  in  the  ton  of  tankage  would  then  be 
w^orth  $9.60,  making  the  nitrogen  cost  $12.40.  The 
140  pounds  of  nitrogen  in  the  ton  of  fertilizer  would 
then  be  worth  $12.40,  or  8.8  cents  per  pound.  In 
eastern  markets  the  price  of  tankage  is  usually  much 
higher  than  near  the  large  packing  houses  of  the  west. 

153.  Flesh  Meal.  —  The  flesh  refuse  from  slaugh- 
ter-houses is  sometimes  kept  separate  from  the  tank- 
age and  sold  as  flesh  meal,  the  fat  and  gelatin  being 


132  SOILS   AND    FERTILIZERS 

first  removed  and  used  for  the  manufacture  of  glue  and 
soap.  Flesh  meal  is  variable  in  composition  and  may 
be  very  slow  in  decomposing.  It  contains  from  4  to 
8  per  cent,  or  more  of  nitrogen  with  an  appreciable 
amount  of  phosphoric  acid.  Occasionally  it  is  used 
for  feeding  poultry  and  hogs,  and  cattle  to  a  limited 
extent.  When  thus  used  the  fertilizer  value  of  the 
dung  is  nearly  equivalent  to  the  original  value  of  the 
meal. 

154.  Fish  Scrap.  — The  flesh  of  fish  is  very  rich  in 
nitrogen. '♦^  The  offal  parts,  as  heads,  fins,  tails,  and  in- 
testines, are  dried  and  prepared  as  a  fertilizer.  Many 
species  of  fish  which  are  not  edible  are  caught  in  large 
numbers  to  be  used  for  this  purpose.  In  sea-coast 
regions  fish  fertilizer  is  one  of  the  cheapest  and  best  of 
the  nitrogenous  manures.  It  is  richer  in  nitrogen 
than  tankage  or  flesh  meal,  and  in  many  cases  equal 
to  dried  blood.  It  readily  undergoes  nitrification  and 
is  a  quick-acting  fertilizer. 

155.  Seed  Residues.  —  Many  seeds,  as  cottonseed 
and  flaxseed,  are  exceedingly  rich  in  nitrogen.  When 
the  oil  has  been  removed,  the  flaxseed  and  cottonseed 
cake  are  proportionally  richer  in  nitrogen  than  the 
original  seed.  This  cake  is  usually  sold  as  cattle 
food,  but  occasionally  used  as  fertilizer.  Cotton- 
seed cake  contains  from  6  to  7  per  cent,  of  nitro- 
gen, and  compares  fairly  well  in  nitrogen  content  with 
animal  bodies.      Cottonseed   cake  or   meal  is  not  so 


NITROGENOUS    MANURES  I33 

quick-acting  a  fertilizer  as  dried  blood,  but  when  used 
in  southern  latitudes  a  little  time  before  seeding,  the 
nitrogen  becomes  available  for  crop  purposes.  Cot- 
tonseed or  linseed  meal  containing  a  high  per  cent,  of 
oil  is  much  slower  in  decomposing  than  that  which 
contains  but  little  oil.  It  is  orenerallv  considered  bet- 
ter  economy  to  feed  the  cake  to  stock  and  use  the 
manure  than  to  apply  the  cake  directly  to  the  land. 
Of  late  years  cottonseed-meal  has  been  so  reduced  in 
price  that  its  use  as  a  fertilizer  has  been,  admissible. 

A  ton  of  cottonseed-meal  costing  $20  and  contain- 
ing 2  per  cent,  of  phosphoric  acid  and  7  per  cent,  of 
nitrogen  would  be  equivalent  to  buying  the  nitrogen 
at  1 3. 1  cents  per  pound,  which  is  frequently  cheaper 
than  purchasing  some  other  nitrogen  fertilizer. 

156.  Leather,  Wool  Waste  and  Hair  are  rich  in 
nitrogen,  but  on  account  of  their  slow  rate  of  decom- 
posing are  unsuitable  for  fertilizer  purposes.  When 
present  in  fertilizers  they  give  poor  field  results. 

157.  Solubility  of  Organic  Nitrogenous  Mate- 
rials. —  The  method  employed  to  detect,  in  fertilizers, 
the  presence  of  inert  forms  of  nitrogen  as  leather,  is  to 
digest  the  material  in  prepared  pepsin  solution. ^9 
Substances  like  dried  blood  are  nearly  all  soluble  in 
the  pepsin,  while  leather  and  inert  forms  are  only  par- 
tially so.  The  solubility  of  organic  nitrogen  in  pep- 
sin solution  determines,  to  a  great  extent,  the  value  of 
the  material  as  a  fertilizer.  5° 


134  SOILS   AND    FERTILIZERS 

Soluble  in  prepared 

pepsin  solution. 
Per  cent,  of  nitrogen. 

Dried  blood 94.2 

Ground  dried  fish 75.7 

Tankage 73,6 

Cottonseed   meal 86.4 

Hoof  and  horn  meal 30.0 

Leather 16.7 

158.  Peat  and  Muck.  —  ]\Iany  samples  of  peat  and 
muck  are  quite  rich  in  nitrogen.  The  nitrogen  is, 
however,  in  a  very  insohible  form,  and  is  with  diffi- 
culty nitrified.  When  mixed  with  stable  manure, 
particularly  liquid  manure,  with  the  addition  of  a  lit- 
tle lime,  fermentation  may  be  induced,  and  a  valuable 
manure  produced.  Muck  or  peat  should  be  dried  and 
sun-cured,  and  then  used  as  an  absorbent  m  stables. 
Peat  differs  from  muck  in  being  fibrous.  If  the  muck 
gives  an  acid  reaction,  lime  (not  quicklime)  should  be 
used  with  it  in  the  stable,  as  directed  under  farm 
manures.  When  easily  obtained  muck  is  one  of  the 
cheapest  forms  of  nitrogen. 


Composition  of  Muck  Sampe^es.'^ 


Nitrogen. 
Per  cent. 


Marshy  place,  producing  hay 2.21 

Marshy  place,  dry  in  late  summer 2.01 

Old  lake  bottom 1.81 

159.  Leguminous  Crops  as  Nitrogenous  Manures. 

—  The  frequent  use  of  leguminous  crops  for  manurial 
purposes  is  the  cheapest  way  of  obtaining  nitrogen. 
When  the  crop  is   not  removed  from  the  land  but  is 


NITROGENOUS    MANURES  1 35 

plowed  under  while  green,  the  practice  is  called  green 
manuring.  This  does  not  enrich  the  land  with  any 
mineral  material  but  results  in  changing  to  humate 
forms  inert  plant  food.  Green  manuring  should  take 
the  place  of  bare  fallow,  as  its  effects  are  in  many 
respects  more  beneficial.  With  green  manuring, 
nitrogen  is  added  to  the  soil  while  with  bare  fallow 
there  is  a  loss  of  nitrogen.  Leguminous  crops,  as 
clover,  peas,  crimson  clover,  and  cow  peas,  should  be 
made  to  serv^e  as  the  main  source  of  the  nitrogen  for 
crop  production. 

160.  Sodium  Nitrate. —  The  nitric  nitrogen  most 
frequently  met  with  in  commercial  forms  is  sodium 
nitrate,  commonly  known  as  Chili  saltpeter.  It  is  a 
natural  deposit  found  extensively  in  Chili,  Peru,  and 
the  United  States  of  Colombia.  Various  theories  have 
been  proposed  to  account  for  these  deposits,  but  it  is 
difficult  to  determine  just  how  they  have  been  formed.'° 
Their  value  to  agriculture  may  be  estimated  from  the 
fact  that  there  are  annually  used  in  the  United  States 
about  100,000  tons,  and  in  Europe  about  700,000  tons. 
The  commercial  value  of  nitrogen  in  fertilizers  is  reg- 
ulated by  the  price  of  sodium  nitrate  which,  when  pure, 
contains  16.49  P^^  cent,  of  nitrogen.  Commercial 
sodium  nitrate  is  from  95  to  97  per  cent.  pure. 
An  ordinary  sample  contains  about  16  per  cent, 
of  nitrogen  and  costs  from  $50  to  $60  per  ton,  making 
the  nitrogen  worth  from   15   to  18  cents  per    pound. 


136  SOILS    AND    FERTILIZERS 

Sodium  nitrate  is  the  most  active  of  all  the  nitrogenous 
manures.  It  is  soluble  and  does  not  have  to  undergo 
the  nitrification  process  before  being  utilized  by  crops. 
On  account  of  its  extreme  solubility  it  should  be  ap- 
plied sparingly,  for  it  cannot  be  retained  in  the  soil. 
As  a  top  dressing  on  grass,  it  will  respond  by  impart- 
ing a  rich  green  color.  It  may  be  used  at  the  rate  of 
250  pounds  per  acre,  but  a  much  lighter  application 
will  generally  be  found  more  economical.  Sodium 
nitrate  may  contain  traces  of  sodium  perchlorate, 
which  is  destructive  to  vegetation,  if  the  fertilizer  is 
used  in  excess.^'  Sodium  nitrate,  in  small  amounts, 
is  the  fertilizer  most  frequently  resorted  to  when  the 
forcing  of  crops  is  desired  as  in  early  market  garden- 
ing. Its  use  for  fertilizing  horticultural  crops  has  be- 
come equally  as  extensive  as  for  general  farm  crops. 
Excessive  amounts  of  sodium  nitrate  may  produce  in- 
jurious results.  It  stimulates  a  rank  growth  of  dark 
green  foliage,  and  retards  the  maturity  of  plants,  but 
when  properly  used  it  is  one  of  the  most  valuable  of 
the  nitrogenous  fertilizers. 

161.  Ammonium  Salts.  —  iVmmonium  sulphate  is 
obtained  as  a  by-product  in  the  manufacture  of  illumi- 
natino^  gras  and  is  extensivelv  sold  as  a  fertilizer.  It 
usually  contains  about  20  per  cent,  of  nitrogen,  equiv- 
alent to  95  per  cent,  of  ammonium  sulphate,  the  re- 
maining 5  per  cent,  being  moisture  and  impurities. 
Ammonium   sulphate  is  not  generally  considered  the 


NITROGENOUS   MANURES  137 

equivalent  of  sodium  nitrate.  It  is,  however,  a  valua- 
ble form  of  nitrogen.  The  statements  made  regarding 
the  use  of  sodium  nitrate  apply  equally  well  to  the  use 
of  ammonium  sulphate.  Ammonium  chloride  and 
ammonium  carbonate  are  not  suitable  for  fertilizers  on 
account  of  their  destructive  action  upon  vegetation. 

162.  Nitrogen  and  Ammonia  Equivalent  of  Fer- 
tilizers. —  Nitrogenous  fertilizers  are  sometimes 
represented  as  containing  a  certain  amount  of  ammo- 
nia instead  of  nitrogen  ;  this  is  so  that  a  higher  per- 
centage may  be  made  to  appear.  Fourteen-seven- 
teenths  of  ammonia  is  nitrogen,  and  if  a  fertilizer  is 
said  to  contain  2.25  per  cent,  ammonia,  it  is  equiva- 
lent to  1.85  per  cent,  of  nitrogen. 

163.  Purchasing  Nitrogenous  Manures. — In  pur- 
chasing nitrogenous  manure,  the  special  purpose  for 
which  it  is  to  be  used  should  always  be  considered. 
Under  some  conditions,  as  forcing  a  crop  on  an  im- 
poverished soil,  sodium  nitrate  is  desirable.  Under 
other  conditions  tankage,  cottonseed  cake,  or  some  * 
other  form  of  nitrogen  may  be  made  to  answer  the 
purpose.  There  is  annually  expended  in  purchasing 
nitrogenous  fertilizers  a  laro;e  amount  of  monev  which 
could  be  expended  more  economically,  if  the  science 
of  fertilizing  were  given  a  more  careful  study. 


CHAPTER  V 


FIXATION 

164.  Fixation,  a  Chemical  Change. — When  a  fertil- 
izer is  applied  to  a  soil  chemical  changes  take  place 
between  the  soil  and  the  fertilizer.  Theie  is  a  general 
tendency  for  the  sohible  matter  of  fertilizers  to  iinderg^o 
chemical  changes  and  become  insoluble.  This  pro- 
cess is  known  as  fixation.  If  a  solution  of  potassium 
chloride  be  percolated  through  a  column  of  clay,  the 
filtrate  will  contain  scarcely  a  trace  of  potassium  chlo- 
ride, but  instead  calcium  and  other  chlorides.  In  its 
action  upon  the  soil,  the  potassium  chloride  has  un- 
dergone a  chemical  change,  the  element  potassium 
being  replaced  by  the  element  calcium.  An  ex- 
change has  taken  place  between  the  two  bases. 

165.  Fixation  Due  to  Zeolites.  —  It  has  been  shown 
by  experiments,  particularly  by  Way  and  Voechler, 
that  fixation  is  due  mainly  to  the  zeolitic  silicates.^^ 
Sandy  soils  containing  but  little  clay  have  only  a  fee- 
ble power  of  fixation.  Clay  soils  when  digested  with 
hydrochloric  acid  to  remove  the  zeolitic  silicates,  lose 
their  power  of  fixation.  The  fixation  of  potassium 
chloride  and  the  liberation  of  calcium  chloride  may  be 
illustrated  by  the  following  reaction  : 


FIXATION  139 

A1,,0,  ^  A1,0,  1 

^^^^  U.(SiO,)..H,0-r2HCl  =p^^o,  [x(SiO,)..H,0  -^  CaCl,. 
etc.    J  etc.    J 

166.  Humus  May  Cause  Fixation.  —  Other  com- 
pounds of  the  soil  as  humus  and  calcium  carbonate 
may  also  take  an  important  part  in  fixation.  In  the 
case  of  humus  a  union  takes  place  between  the  basic 
material  and  the  organic  matter   of  the  soil. 

167.  Soils  Possess  Different  Powers  of  Fixation.  — 
All  soils  do  not  possess  the  power  of  fixation  to  the 
same  extent.  Heavy  clays  have  the  greatest  fixative 
power  while  sandy  soils  have  the  least.  Experiments 
have  shown  that  in  the  first  nine  inches  of  soil  from 
2,000  to  8,000  pounds  per  acre  of  potash  and  phos- 
phoric acid  may  undergo  fixation. ^3  Hence  it  is  that 
a  fertilizer,  after  being  applied  to  a  soil,  may  be  en- 
tirely changed  in  composition,  so  that  the  plant  feeds 
on  the  chemical  compounds  formed,  rather  than  on  the 
original  fertilizer. 

168.  Nitrates  Cannot  Undergo  Fixation.  —  Nitro- 
gen in  the  form  of  nitrates  or  nitrites  cannot  undergo 
fixation.  This  is  because  all  of  the  ordinary  forms  of 
nitrates  are  soluble.  If  potassium  nitrate  be  added  to 
a  soil,  calcium  nitrate  wili  doubtless  be  obtained  as  the 
soluble  compound.  The  potassium  undergoes  fixa- 
tion, but  the  nitrate  radical  does  not.  Chlorides  are 
likewise  incapable  of  undergoing  fixation. 

169.  Fixation  May  Make  Plant  Food  Less  Availa- 
ble. —  If  a  liberal  dressing  of  phosphate    fertilizer  be 


I40  SOILS   AND    FERTILIZERS 

applied  to  a  heavy  clay  soil,  the  phosphoric  acid  which 
is  not  utilized  the  first  year  or  two  ma}'  undergo  fixa- 
tion to  such  an  extent  as  to  become  Unavailable  as 
plant  food.  It  is  not  desirable  to  apply  heavy  dress- 
ings of  fertilizers  at  long  intervals  because  of  fixation. 
It  is  always  best  to  make  lighter  applications  and  more 
frequently. 

170.  Fixation,  a  Desirable  Property  of  Soils. —  If  it 
were  not  for  the  process  of  fixation,  soils  in  regions  of 
heavy  rains  would  soon  become  sterile.  On  account 
of  the  plant  food  being  rendered  insoluble,  it  is  re- 
tained in  the  soil.  The  plant  food  which  undergoes 
fixation  is,  as  a  rule,  in  an  available  condition,  unless 
the  soil  be  one  of  unusual  composition.  The  fixation 
of  fertilizers  regulates  the  supply  of  crop  food.  Many 
fertilizers,  if  they  did  not  undergo  this  process,  would 
be  injurious  to  crops.  There  would  be  an  abnormal 
amount  of  soluble  alkaline  or  acid  compounds  which 
would  be  destructive.  The  process  of  fixation  first 
taking  place  removes,  to  a  great  extent,  the  water-solu- 
ble salts,  particularly  when  the  reaction  is  one  of 
union  rather  than  replacement.  Then  the  plant  is 
free  to  render  soluble  its  own  plant  food  in  quantities 
and  at  times  desired. 

Farm  manures  and  commercial  fertilizers  alike  un- 
dergo the  process  of  fixation  and,  in  studying  fertilizers, 
their  action  upon  the  soil  and  the  products  of  fixation 
are  matters  of  prime  importance. 


•     CHAPTER  VI 

FARM  MANURE 

171.  Variable   Composition   of  Farm  Manures.  — 

The  term  '  farm  manure'  does  not  designate  a  prod- 
uct of  definite  composition.  Manure  is  the  most 
variable  in  chemical  composition  of  any  of  the  mate- 
rials produced  on  the  farm.  It  may  contain  a  large 
amount  of  straw,  in  which  case  it  is  called  coarse  ma- 
nure ;  or  it  may  contain  only  the  solid  excrements  and 
a  little  straw,  the  liquid  excrements  being  lost  by 
leaching  ;  then  again  it  may  consist  of  the  droppings 
of  poorly  fed  animals,  or  of  the  mixed  excrements  of 
different  classes  of  well-fed  animals. 

The  term  '  stable  manure'  has  been  proposed  for 
that  product  which  contains  all  of  the  solid  and  liquid 
excrements  with  the  necessary  absorbent,  before  any 
losses  have  been  sustaii^ed.'^  The  term  '  barnyard 
manure'  is  restricted  to  that  material  which  ac- 
cumulates around  some  barns  and  farm  vards,  and  is 
exposed  to  leaching  rains  and  the  drying  action  of  the 
sun. 

172.  Average  Composition  of  Manures.  —  The  solid 
excrements  of  animals  contain  from  6crto  85  per  cent, 
of  water  ;  when  mixed  with  straw,  and  the  liquid 
excrements    are  retained,   the    mixed    manure     con- 


142 


SOILS   AND    FERTILIZERS 


tairts  about  75  per  cent,  of  water.  The  nitrogen  va- 
ries from  0.4  to  0.9  per  cent. ,  according  to  the  natnre  of 
the  food  and  the  extent  to  which  other  factors  have  af- 
fected the  composition.  In  general,  animals  consu- 
ming liberal  amounts  of  coarse  fodders  produce  manure 


-4.    2.1-3.  ^.z.m 

Fig.  24.     Average  composition  of  Fig.  25.     Manure  after  six 

fresh  manure.  months'  exposure. 

I.  Nitrogen.     2.  Phosphoric  acid. 
3.  Potash. 

with  a  higher  per  cent,  of  potash  than  of  phosphoric 
acid.  This  is  because  the  potash  in  the  food  exceeds 
the  phosphoric  acid.  The  average  composition  of 
mixed  stable  manure  is  about  as  follows  : 


Average. 
Per  cent. 


Nitrogen 0.50 

Phosphoric  acid 0.35 

Potash 0.50 


Range. 
Per  cent. 

0,4  to  0.8 

0.2  to  0.5 

0.3  to  0.9 


In  calculating  the  amount  of  fertility  in  manures,  it 
is  more  satisfactory  to  compute  the  \'alue  from  the  food 
consumed  and  the  care  which  the  manure  has  received, 
than  to  use  figures  expressing  average  composition. 


FARM    MANURE  I43 

173.  Factors  which  Influence  the  Composition  and 
Value  of  Manure.  — 

I.  Kind  and  amount  of  absorbents  used. 

II.  Kind  and  amount  of  food  consumed. 

III.  Age  and  kind  of  animals. 

IV.  Methods  employed  in  collecting,  preserving 
and  utilizing  the  manure. 

Any  one  of  the  above,  as  well  as  many  minor  factors, 
may  influence  the  composition  and  value  of  stable 
manure. 

174.  Absorbents.  —  The  most  universal  absorbent 
is  straw.  Wheat  straw  and  barley  straw  have  about 
the  same  manurial  value.  Oat  straw,  however,  is 
more  valuable.  The  average  composition  of  straw 
and  other  absorbents  is  as  follows : 

straw.  Leaves.  Peat.  Sawdust. 

Per  cent.  Per  cent.  Per  cent.  Per  cent. 

Nitrogen 0.40            0.6  i.o            o.i 

Phosphoric  acid 0.36            0.3  ..             0.2 

Potash 0.80            0.3  ..             0.4 

When  a  large  amount  of  straw  is  used  the  per  cent, 
of  nitrogen  and  phosphoric  acid  is  decreased,  while  the 
per  cent,  of  potash  is  slightly  increased.  Sawdust 
and  leaves  both  make  the  manure  more  dilute.  Dry 
peat  makes  the  manure  richer  in  nitrogen.  The  ab- 
sorbent powers  of  these  different  materials  are  about  as 
follows  :'3 


144  SOILS   AND    FERTILIZERS 

Per  cent,  of 
water  absorbed. 

Fine  cut  straw 30.0 

Coarse  uncut  straw 18.0 

Peat 60.0 

Sawdust   45.0 

The  proportion  of  absorbents  in  mannre  ranges  from 
a  fifth  to  a  third  of  the  total  weight  of  the  mannre. 

175.  Use  of  Peat  and  Muck  as  Absorbents.  —  On 

acconnt  of  the  high  per  cent,  of  nitrogen  in  peat  and 
the  power  which  it  possesses  when  dry  of  absorbing 
water,  it  is  a  vahiable  material  to  use  as  an  absorbent 
in  stables.  As  previously  explained,  peat  is  slow  of 
decomposition,  but  when  mixed  with  the  liquid  ma- 
nure it  readily  yields  to  fermentation,  particularly  if  a 
little  land  plaster  or  marl  be  used  in  the  stable  along 
with  the  peat;  Peat  has  a  high  absorptive  power  for 
gases  as  well  as  liquids,  and  when  used  stables  are  ren- 
dered particularly  free  from  foul  odors. 
RELATION  OF  FOOD  CONSUMED  TO  MANURE  PRODUCED 

176.  Bulky  and  Concentrated  Foods.  —  The  more 
concentrated  and  digestible  the  food  consumed,  the 
more  valuable  is  the  manure.  Coarse  bulky  fodders 
always  give  a  large  amount  of  a  poor  quality  of  ma- 
nure. For  example,  the  manure  from  animals  fed  on 
timothy  hay  and  that  from  animals  fed  on  clover  hay 
and  grain,  show  a  wide  difference  in  composition. 
The  dry  matter  of  timothy  hay  is  about  55  per  cent, 
digestible.     From  a  ton  of  timothy  hay  there  will  be 


FOOD  CONSUMED  TO  MANURE  PRODUCED  I45 

about  792  pounds  of  dry  matter  in  the  manure.  The 
nitrogen,  phosphoric  acid,  and  potash  in  the  food  con- 
sumed are  nearly  all  returned  in  the  manure,  except 
under  those  conditions  which  will  be  noted.  The 
manure  from  a  ton  of  mixed  feed,  as  clover  and  bran, 
will  be  smaller  in  amount  but  more  concentrated  than 
that  produced  from  timothy.  In  a  ton  of  timothy  and 
in  a  ton  of  mixed  feed  (1500  lbs.  clover,  500  lbs.  bran) 
there  are  present : 

Timothy.  Mixed  feed. 

Lbs.  Lbs. 

Nitrogen 25.0  40.0 

Phosphoric  acid 9.0  24.0 

Potash 40.0  30.0 

The  nitrogen,  phosphoric  acid,  and  potash  in  these 
tw^o  rations  are  retained  in  the  animal  bodies  in  dis- 
similar amounts ;  that  is,  10  per  cent,  more  of  these 
elements  are  retained  from  the  more  liberal  ration,  due 
to  more  favorable  conditions  for  o^rowth.  ^Making-  al- 
lowance  for  this  fact  there  will  be  present  in  the  ma- 
nure from  the  mixed  feed  one-half  more  nitrogen,  and 
two  and  one-half  times  as  much  phosphoric  acid,  as 
in  the  manure  from  the  timothy  hay,  which,  free 
from  bedding,  contains  about  792  pounds  of  indigesti- 
ble matter  while  that  from  the  mixed  feed  con- 
tains 760  pounds,  the  mixed  ration  being  more  digesti- 
ble. If  both  manures  contain  the  same  amount  of  ab- 
sorbents, the  manure  from  the  ton  of  mixed  clover 
and  bran  will  weigh  slightly  less,  but  contain  more 
fertilitv  than  that  from  the  timothv  hav. 


146  SOILS   AND    FERTILIZERS 

The  value  of  the  manure  can  be  approximately  de- 
termined from  the  composition  of  the  food  consumed. 
Only  a  small  amount  of  the  nitrogen  in  the  food  is  re- 
tained in  the  body.  The  larger  portion  is  used  for  re- 
pair purposes.  The  nitrogen  of  the  tissues  which 
have  been  renewed  is  voided  as  urea  in  the  liquid  ex- 
crements. Some  of  the  nitrogenous  compounds  of  the 
food  are  utilized  for  the  production  of  fat,  in  which 
case  the  nitrogen  is  voided  in  the  excrements.  The 
fact  that  but  little  of  the  nitrogen  of  the  food,  under 
lYiost  conditions,  is  retained  in  the  body  may  be  ob- 
served from  the  figures  of  Lawes  and  Gilbert  relating 
to  the  composition  of  the  flesh  added  to  animals  while 
undergoing  the  fattening  process. ^^ 

Increase  during  Fattening. 

Dry  Nitrogenous 

Water.  matter.  Fat.  matter.  Ash. 

Ox 24.6  75.4  66.2  7.69  1.47 

vSheep 20.1  79,9  70.4  7.13  2.36 

Pigs 22.0  78.0  71.5  6.44  0.06 

The  results  of  numerous  digestion  experiments 
show  that  when  the  food  undergoes  digestion  from  5 
to  15  per  cent,  of  the  nitrogen  is,  as  a  rule,  retained  in 
the  bod}'.  The  nitrogen  of  the  food  is  utilized  largely 
to  replace  that  which  has  been  required  for  vital  func- 
tions. The  nitrogen  of  the  food  enters  the  body,  un- 
dergoes digestion  changes,  is  utilized  for  some  vital 
function,  and  is  then  voided  in  the  excrements. 

The  digestion  of  the  food  has  been  compared  to  the 


FOOD  CONSUMED  TO  MANURE  PRODUCED  147 

combustion  of  fuel :  the  undigested  products  of  the 
solid  excrements  represent  the  ashes,  and  the  urine 
represents  the  volatile  products.  When  wood  is 
burned  the  nitrogen  is  converted  into  volatile  products. 
When  food  is  digested  and  utilized  by  the  body  the  di- 
gestible nitrogen  is  mainhv  converted  into  urea,  while 
the  undigestible  nitrogen  is  voided  in  the  dung. 

177.  Composition  of  Solid  and  Liquid  Excrements 
Compared.  —  In  composition  the  liquid  excrements 
differ  from  the  solids  in  having  a  much  larger  amount 
of  nitrogen  and  less  phosphoric  acid.^s 

Water.  Nitrogen.  Phosphoric  acid.  Potash. 

Solids.  Liquids.     Solids.     Liquids.        Solids.     Liquids.        Solids. 
Percent.  Per  cent.  Percent.  Percent.    Per  cent.  Percent.    Per  cent. 

Cows..  76  89  0.50  1.20  0.35  ...  0.30 

Horses.  84  92  0.30  0.86  0.25  ...  o.io 

Pigs...  80  97.0  0.60  0.80  0.45  0.12  0.50 

Sheep  .  58  86.5  0.75  1.40  0.60  0.05  0.30 

The  nitrogen  of  the  food  consumed  influences  the 
amount  of  water  in  the  manure.  As  a  rule,  a  highly 
concentrated  nitrogenous  ration,  produces  a  higher  per 
cent,  of  water  in  the  manure  than  a  well-balanced 
ration.  There  is  but  little  phosphoric  acid  in  the 
liquid  excrements  of  horses  and  cows,  while  the  urine 
of  sheep  and  swine  contains  appreciable  amounts  of 
this  element. 

The  liquid  manure  is  more  constant  both  in  compo- 
sition and  amount  than  the  solid  excrements.  This 
fact  may  be  observed  from  the  following  table,  which 
gives   the   composition  of  the  solid   and  liquid  excre- 


148 


SOILS   AND    FERTILIZERS 


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FOOD  CONSUMED  TO  MANURE   PRODUCED  I49 

ments   from   hog^s  when   fed  on  different  amounts  of 


gram 


56 


The  amount  of  waste  matter  in  the  urine  is  nearly 
the  same  whether  an  animal  be  gaining  or  losing  in 
flesh,  consequently  the  urine  is  more  constant  in  both 
composition  and  quantity  than  the  solid  excrements. 

The  amount  and  composition  of  the  solid  excre- 
ments vary  with  the  amount  and  kind  of  food  con- 
sumed. If  the  food  is  indigestible  the  solid  excrements 
contain  a  larger  part  of  the  nitrogen  as  indigestible 
protein.  When  the  body  is  properh-  supplied  with 
food  for  all  purposes,  normal  conditions  exist,  and  the 
amount  of  nitrogen  voided  in  the  liquid  and  solid  ex- 
crements is  no  more  than  that  supplied  in  the  food 
consumed. 

178.  Manurial  Value  of  Foods.  —  The  manurial 
value  of  fodder  is  determined  by  the  amount  of  nitro- 
gen, phosphoric  acid,  and  potash  present  in  the  material. 
Timothy  hay,  for  example,  has  a  manurial  value  of 
$5.30  per  ton,  which  means  that  if  the  nitrogen,  phos- 
phoric acid,  and  potash  in  the  timothy  hay  were  pur- 
chased in  commercial  forms  they  w^ould  cost  $5.30. 
Lawes  and  Gilbert  estimate  that  80  per  cent,  of  the 
fertility  in  fodders  is,  as  a  rule,  returned  in  the  ma- 
nure. 

In  the  following  table  are  given  the  pounds  of 
nitrogen,  phosphoric  acid,  and  potash  per  ton  of  ma- 
terial :" 


150  SOILS   AND    FERTILIZERS 

Nitrogen.      Phosphoric  acid.     Potash. 

Lbs.  Lbs.  Lbs. 

Timothy  hay 25  9  40 

Clover  hay 45  14  30 

Wheat  straw 11  4  12 

Oat  straw 12  4  18 

Wheat    45  20  12 

Oats 33  16  II 

Barley 40  18  il 

Rye 42  20  13 

Flax 87  32  14 

Com 32  14  8 

Wheat  Shorts 48  31  20 

Wheat  Bran 54  52  30 

Oil  meal 100  35  25 

Cottonseed  meal 130  35  56 

Milk 10  3  3 

Cheese 90  23  5 

Live  cattle 53  37  3 

Potatoes 7  3  II 

Butter I  I  I 

Live  pigs 40  17  3 

179.  Commercial  Value  of  Manures.  —  When  the 
value  of  farm  manure  is  calculated  on  the  same  basis 
as  that  of  commercial  fertilizers  it  will  be  found  that 
stable  manure  is  worth  from  $2  to  $3.50  per  ton.  The 
value  of  the  increased  crop  resulting  from  the  use  of 
manure  will  vary  with  conditions.  It  is  sometimes 
stated  that  the  phosphoric  acid  and  potash  in  stable 
manures  is  not  as  soluble  as  that  in  commercial  fer- 
tilizers, and  consequently  it  is  w^orth  less.  While  not 
so  soluble  in  the  form  of  manure,  it  frequently  hap- 


AGE    AND    KIND    OF    ANIMAL  151 

pens  that  the  phosphoric  acid  and  potash  in  the  com- 
mercial fertilizers  become,  through  fixation  processes, 
less  soluble  when  mixed  with  the  soil  than  the  same 
elements  in  stable  manure. 

Stable  manure  is  valuable  not  only  for  the  fertility 
contained  but  also  because  it  makes  the  inert  plant 
food  of  the  soil  more  available  and  exercises  such  a 
favorable  influence  on  the  water  supply  of  crops;  hence 
it  is  justifiable  to  assign  the  same  value  to  the  ele- 
ments in  well-prepared  farm  manures  as  to  those  in 
commercial  fertilizers. 

If  well-prepared  stable  manure  is  not  worth  $2.50 
per  ton,  then  too  much,  accordingly,  is  paid  for  com- 
mercial forms  of  plant  food. 

INFLUENCE  OF  AGE  AND  KIND  OF  ANIMAL 

180.  Manure  from  Young  and  Mature  Animals.  — 

The  manure  from  older  animals  is  more  valuable  than 
that  from  young  animals,  even  when  fed  the  same 
kind  of  food.  This  is  because  more  of  the  phosphoric 
acid  and  nitrogenous  matters  are  retained  in  the  body 
of  a  vounof  animal.  It  is  not  so  much  a  difference  in 
digestive  power  as  a  difference  in  retentive  power.  In 
older  animals  the  proportion  of  new  nitrogenous  tissue 
produced  is  much  less  than  in  young  animals,  and 
more  of  the  nitrogen  of  the  food  is  used  for  repair  pur- 
poses and  subsequeptly  voided  in  the  manure,  while 
with  younger  animals  more  of  the  nitrogen  of  the  food 
is  retained  for  the  construction  of  new  muscular  tissue. 


152  SOILS   AND    FERTILIZERS 

The  difference  in  composition  between  the  manure  of 
old  and  of  young  animals  is  not,  however,  so  great  as 
might  appear. 

When  an  animal  is  neither  gaining  nor  losing  in 
flesh,  and  is  not  producing  milk,  an  equilibrium  is 
established  betw^een  the  nitrogen  in  the  food  supply 
and  the  nitrogen  in  the  manure.  Under  such  condi- 
tions practically  all  of  the  nitrogen  of  the  food  is  re- 
turned in  the  manure. ^^ 

i8i.  Cow  Manure.  —  A  milch  cow  when  fed  a  bal- 
anced ration,  wall  make  from  60  to  70  pounds  of  solid 
and  liquid  manure  a  day,  of  which  20  to  30  pounds  are 
liquid  excrements.  The  solid  excrements  contain 
about  6  pounds  of  dry  matter.  When  a  cow  is  fed 
clover  hay,  corn  fodder,  and  grain,  about  half  of  the 
nitrogen  of  the  food  is  in  the  urine,  about  one-fourth 
in  the  milk,  and  the  remainder  in  the  solid  excre- 
ments. Hence,  if  the  solid  excrements  only  are  col- 
lected, but  a  quarter  of  the  nitrogen  of  the  food  is  ob- 
tained, while  if  both  solids  and  liquids  are  utilized 
three-quarters  of  the  nitrogen  is  secured.  Cow  manure 
is  extremely  variable  in  composition,  and  is  the  most 
bulky  of  any  manure  produced  by  domestic  animals. 
A  well-fed  cow  will  produce  about  80  lbs.  of  manure 
per  day,  including  absorbents. 

182.  Horse  Manure.  —  Horse  manure  contains  less 
water  than  cow  manure,  and  is  of  a  more  fibrous 
nature,  doubtless    due    to    the    horse    possessing    less 


AGE    AND    KIND    OF    ANIMAL  I53 

power  for  digesting  cellulose  materials.  Horse  ma- 
nure readily  ferments  and  gives  off  ammonia  products. 
When  the  manure  becomes  dry,  fire-fanging  results, 
due  to  rapid  fermentation  followed  by  the  growth  of 
fungus  bodies.  Horse  manure  is  generally  considered 
of  but  little  value.  This  is  because  it  so  readilv  de- 
teriorates  in  value  and  when  used  it  has  frequently 
lost  much  of  its  nitrogen  by  fermentation.  When 
mixed  with  cow  manure,  both  manures  are  improved, 
the  rapid  fermentation  of  the  horse  manure  is  checked, 
and  at  the  same  time  the  cow  manure  is  improved  in 
texture.  It  is  estimated  that  horses  void  about  three- 
fifths  of  their  manure  in  the  stable.  A  well-fed  horse 
at  ordinarily  hard  work  will  produce  about  50  pounds 
of  manure  per  day,  of  which  about  one-fourth  is  urine. 
A  horse  will  produce  about  6  tons  of  manure  per  year 
in  the  stable.  If  properly  preserved  and  used  it  is  a 
valuable,  quick-acting  manure,  but  if  allowed  to  fer- 
ment and  leach  it  will  give  poor  results. 

183.  Sheep  Manure. — Sheep  produce  a  small 
amount  of  concentrated  manure,  containing  less  water 
than  that  produced  by  any  other  domestic  animal.  It 
readily  ferments  and  is  a  quick-acting  fertilizer. 
When  mixed  with  horse  and  cow  manure  the  mixture 
ferments  more  evenly.  Because  of  the  small  amount 
of  water,  sheep  manure  is  very  concentrated  in  composi- 
tion. It  is  valuable  for  general  gardening  purposes,  or 
whenever  a  concentrated  quick-acting  manure  is  desired. 


154  SOILS   AND    FERTILIZERS 

184.  Hog  Manure.  —  The  composition  of  hog  ma- 
nure is  exceedingly  variable  on  account  of  the  varied 
character  of  the  food  consumed.  The  manure  from 
fattening  hogs  which  are  well  fed  compares  very  fa- 
vorably in  composition  and  value  with  the  manure 
produced  by  other  animals.  It  contains  a  high  per 
cent,  of  water,  and,  like  cow  manure,  may  be  slow 
in  decomposing.  From  a  given  weight  of  grain,  pigs 
produce  less  dry  matter  in  the  manure  than  sheep  or 
cows.  The  liquid  excrements  of  well-fed  hogs 
are  rich  in  nitrogen,  containing,  on  an  average,  about  2 
per  cent.  On  account  of  hog  manure  containing  so 
much  water,  losses  by  leaching  readily  occur.  The 
solid  excrements  when  leached  and  deprived  of  the 
liquid  excrements  have  but  little  value  as  a  fertilizer. 

185.  Hen  Manure.  —  Like  all  other  farm  manures 
hen  manure  is  variable  in  composition.  The  nitrogen 
is  present  mainly  in  the  form  of  ammonium  com- 
pounds. This  makes  it  a  quick-acting  fertilizer. 
When  fowls  are  well  fed  the  manure  contains  about 
the  same  amount  of  nitrogen  as  sheep  manure.  Hen 
manure  readily  ferments,  and  if  not  properly  cared 
for  losses  of  nitrogen,  as  ammonia,  occur.  It  is  not 
advisable  to  mix  hard  wood  ashes  or  ordinary  lime 
with  hen  manure  because  the  ammonia  is  so  readily 
liberated  by  alkaline  compounds.  The  value  of  hen 
manure  is  due  to  its  being  a  quick-acting  fertilizer 
rather  than  to  its  containing  such   a  large  amount  of 


AGE    AND    KIND    OF    ANIMAL  1 55 

fertility.  A  hen  produces  about  a  bushel  of  manure 
per  year.  55 

Composition  of  Hen  Manure. 

Per  cent. 

Water 57-50 

Nitrogen 1.27 

Phosphoric  acid 0.82 

Potash o.  28 

186.  Mixing  of  Solid  and  Liquid  Excrements.  — 

The  solid  and  liquid  excrements,  when  properly  mixed, 
make  a  well-balanced  manure.  The  urine  alone  is  not 
a  complete  manure,  as  it  is  deficient  in  phosphoric  acid 
and  other  mineral  matter.  The  solid  excrements  and 
the  urine,  when  mixed  with  soil,  readily  undergo  nitri- 
fication. The  nitrogen  in  the  solid  excrements  is  in 
the  form  of  indigestible  protein,  and  is  rendered  avail- 
able as  plant  food  more  slowdy.  Land  which  has 
been  heavily  dressed  with  leached  manure  has  re- 
ceived an  unbalanced  manure,  and  is  deficient  in 
nitrogen  but  fairly  well  supplied  with  mineral  matter. 
Such  a  soil  may  fail  to  respond  because  of  the  unbal- 
anced character  of  the  manure. 

187.  Volatile  Products  from  Manure.  —  The  fer- 
mentation of  maniire  in  stables  may  cause  the  pro- 
duction of  a  large  number  of  volatile  compounds.  The 
ammonia  and  nitrogen  compounds  are  products  which 
cause  losses  of  value  to  the  manure.  Urea,  when  it 
ferments,  produces  ammonia  or  ammonium  carbonate. 
If  ammonia  is  produced  it  combines  with  the  carbon 


156  SOILS   AND    FERTILIZERS 

dioxide,  which  is  always  present  in  stables  in  liberal 
amounts  as  a  product  of  respiration,  and  forms  ammo- 
nium carbonate,  a  volatile  compound.  When  the 
stable  atmosphere  becomes  charged  with  ammonium 
carbonate,  some  of  it  is  deposited  on  the  walls  of  the 
stable,  forming  a  white  coating.  The  white  coating 
found  on  harnesses  and  carriages  stored  in  poorly  ven- 
tilated stables,  is  ammonium  carbonate.  Accumula- 
tions of  manure  in  the  stable  and  poor  ventilation  are 
the  conditions  favorable  to  the  production  of  this  com- 
pound. 

188.  Human  Excrements.  —  The  use  of  human  ex- 
crements as  manure  is  sometimes  advised,  and  in  some 
countries  they  are  extensively  used.  When  fresh,  human 
excrements  may  contain  a  high  per  cent,  of  nitrogen 
and  phosphoric  acid  ;  when  fermented,  a  loss  of  nitro- 
gen occurs.  Heiden  estimates  that  in  a  year  1,000 
pounds  of  excrements  per  person  are  made,  which  con- 
tain $2.25  worth  of  fertility. 5^  For  sanitary  reasons, 
human  excrements  should  be  used  with  great  care. 
It  is  doubtful  with  the  abundance  and  cheapness  of 
plant  food  whether  their  extensive  use  as  manure  is 
advisable.  About  1840,  Liebig  feared  that  the  essen- 
tial elements  of  plant  food  would  accumulate  in  the 
vicinity  of  large  cities  and  be  wasted,  and  that  in  time 
there  would  be  a  decline  in  fertility  due  to  this  cause.59 
Many  political  economists  shared  the  same  fear. 
Since  that  time   the  fixation  of  atmospheric  nitrogen 


PRESERVATION    OF    MANURE  157 

through  the  agency  of  leguminous  crops,  the  exten- 
sive beds  of  sodium  nitrate,  phosphate  rock,  and  Stas- 
furt  salts,  have  been  discovered,  and  larger  areas  of 
more  fertile  soil  have  been  brought  under  cultivation, 
so  that  it  is  not  now  considered  so  essential  to  devise 
means  for  utilizing  human  excrements  as  manure. 

THE  PRESERVATION  OF  MANURE 

189.  Leaching.  —  Leaching  of  manure  is  the  great- 
est source  of  loss.  Experiments  by  Roberts  have 
shown  that  when  horse  manure  is  thrown  in  a  loose 
pile  and  subjected  to  the  joint  action  of  leaching  and 
weathering  it  may  lose  nearly  60  per  cent,  of  its  most 
valuable  fertilizing  constituents  in  six  months.  The 
tabular  results  are  as  follows  :^= 

April  25.  Sept.  28.  Loss. 

Lbs.  Lbs.  Per  cent. 

Gross  weight 4,000  i,73o  57 

Nitrogen 19.60  7.79  60 

Phosphoric  acid     ..         14.80  7.79  47 

Potash 36.0  8.65  76 

Value  per  ton 12. 80  |;i.o6 

Cow  manure,  on  account  of  its  more  compact  nature, 
does  not  leach  so  readily  as  horse  manure.  A  similar 
experiment  with  cow  manure,  conducted  at  the  same 
time,  showed  the  following  losses : 

April  25.  Sept.  28.  Loss. 

Lbs.  Lbs.  Per  cent. 

Gross  weight 10,000  5,125  49 

Nitrogen 47  28  41 

Phosphoric  acid  . .  32  26  19 

Potash 48  44  8 

Value  per  ton I2.29  |i.6o 


158  SOILS   AND    FERTILIZERS 

When  mixed  cow  and  horse  manure  was  compacted 
and  "placed  in  a  galvanized  iron  pan  with  a  perfo- 
rated bottom"  for  six  months,  the  losses  were  as  fol- 
lows : 

March  29.  Sept.  30.  Loss. 

Lbs.  Lbs.  Percent. 

Gross  weight 226  222 

Nitrogen 1.04  i.oi  3.2 

Phosphoric  acid • .       0.61  0.58  4.7 

Potash 1.20  0,43  35.0 

Value  per  ton $2,38  12.16 

190.  Losses  by  Fermentation.  —  When  rapid  fer- 
mentation takes  place  in  manure,  appreciable  losses  of 
nitrogen  may  occur.  When  the  manure  is  well  com- 
pacted and  the  pile  is  so  constructed  as  to  prevent  the 
rapid  circulation  of  air  through  the  pile,  the  losses  are 
reduced  to  the  minimum.  Experiments  have  shown 
that  when  leaching  is  prevented,  the  losses  of  nitrogen 
by  the  fermentation  of  mixed  manure  are  very 
small.  Under  unfavorable  conditions  the  losses 
by  fermentation  may  exceed  15  per  cent.  Hen  ma- 
nure, sheep  manure,  and  horse  manure  suffer  the 
greatest  losses  by  rapid  fermentation.  When  extreme 
conditions  follow  each  other  in  succession,  as  exces- 
sive moisture,  drought,  and  high  temperature,  then 
the  greatest  losses  occur. 

191.  Different  Kinds  of  Fermentation.  — The  large 
number  of  organisms  present  in  manure  all  belong  to 
one  of  two  classes :  (i)  aerobic,  or  (2)  anaerobic. 
The  aerobic  ferments   require   an  abundant  supph'  of 


PRESERVATION    OF    MANURE  1 59 

air  in  order  to  carry  on  their  work.  When  deprived 
of  oxygen  they  become  inactive.  The  anaerobic  fer- 
ments require  the  opposite  conditions.  They  become 
inactive  in  the  presence  of  ox}gen  and  can  thrive  only 
when  air  is  excluded.  In  the  center  of  a  well-con- 
structed   manure    pile    anaerobic    fermentation    takes 


Fig.  26.     Fermentation  of  Manure. 

place  while  on  the  surface  aerobic  fermentation  is  act- 
ive. The  anaerobic  ferments  prepare  the  way  for  the 
action  of  the  aerobic  bodies.  When  aerobic  fermenta- 
tion is  completed  the  organic  matter  is  converted  into 
water,  carbon  dioxide,  ammonia,  and  allied  gases. 
From  what  has  been  said  regarding  the  action  of  these 
two  classes  of  ferments  it  is  evident  that  anaerobic 
fermentation  is  the  most  desirable. 

192.  Water  Necessary  for  Fermentation.  —  In  order 
to  produce  the  best  results  in  fermenting  manure 
water  is  necessary.  If  the  manure  becomes  too  dry 
abnormal  fermentation  takes  place.  Water  is  always 
beneficial  on  manure  as  long  as  leaching  is  prevented; 


l6o  SOILS   AND    FERTILIZERS 

it  encourages  anaerobic  fermentation  by  excluding  the 
air.  Excessive  amounts  of  water,  as  that  which  falls 
on  piles  from  the  eaves  of  buildings,  is  more  than  is 
required  for  good  fermentation.  During  a  dry  time  it 
is  beneficial,  if  conditions  admit,  to  water  the  compost 
pile. 

193.  Heat  Produced  during  Fermentation.  —  Dur- 
ing the  active  fermentation  of  horse  manure  and  sheep 
manure,  a  temperature  of  175°  F.  may  be  reached  by 
the  fermenting  mass.  Ordinarily,  however,  the  tem- 
perature of  the  manure  pile  ranges  from  110°  to  130° 
F.  The  highest  temperature  is  reached  near  the  sur- 
face where  fermentation  is  most  rapid.  The  tempera- 
ture of  fermentation  may  be  sufficiently  high  if  the 
manure  is  mixed  with  the  proper  litter  to  cause  spon- 
taneous combustion. 

194.  Composting  Manure  May  Improve  Its  Quality. 

—  When  manure  is  composted  so  that  leaching  and 
rapid  fermentation  do  not  take  place  the  manure  may 
be  improved  in  quality  by  becoming  more  concentra- 
ted. Pound  for  pound,  composted  manure  is  more 
concentrated  than  fresh  manure,  because,  if  properly 
cared  for,  nearly  all  of  the  nitrogen,  phosphoric  acid, 
and  potash  of  the  original  manure  are  obtained  in  a 
smaller  bulk.  A  ton  of  composted  manure  is  obtained 
from  about  2,800  pounds  of  stable  manure. 


PRESERVATION    OF    MANURE  l6l 

Fresh  Composted 

manure.  manure. 

Per  cent.  Per  cent. 

Nitrogen 0.50  0.60 

Phosphoric  acid 0.28  0.39 

Potash 0.60  0.80 

In  composting  manure  it  should  be  the  aim  to  in- 
duce anaerobic  fermentation  bv  excluding-  the  air  and 
retaining  the  water.  This  can  be  best  accomplished 
by  using  mixed  manure  and  making  a  compact  pile, 
capable  of  shedding  water.  The  compost  pile  should 
be  shaded  to  secure  better  conditions  for  fermentation. 
If  the  pile  becomes  offensive  a  little  earth  on  the  sur- 
face will  absorb  the  odors. 

195.  Use  of  Preservatives.  —  The  use  of  preserv^a- 
tives  as  gypsum  and  kainit  have  been  recommended  to 
prevent  fermentation  losses.  Opinions  differ  as  to 
their  value.  ]Moist  gypsum,  when  it  comes  in  contact 
with  ammonium  carbonate,  produces  ammonium  sul- 
phate, a  non-volatile  compound, 

(NH  )  CO   A-  CaSO  =  (NH  )  SO   4^  CaCO  . 

\  4/2  3      ■  4  ^  4-'^2  4  3 

Gypsum  is  used  at  the  rate  of  about  one-half  pound 
per  day  for  each  animal. ^^  Experiments  have  shown 
that  it  may  prevent  a  loss  of  5  per  cent,  of  the  nitro- 
gen of  horse  manure.  It  may  be  safely  sprinkled  -in 
the  stalls  as  it  has  no  action  on  the  feet  of  animals. 
When  gypsum  is  used  as  a  fertilizer  it  is  very  desira- 
ble to  use  it  in  stables.  It  is  not  advisable  to  use 
lime  in  any  other  form  than  the  sulphate.     Unslaked 


l62  SOILS   AND    FERTILIZERS 

lime  will  decompose  manure  and  liberate  ammonia. 
Neither  kainit  nor  gypsum  should  be  used  when  ma- 
nure is  exposed  to  the  leaching  action  of  rains. 
Preservatives  cannot  be  made  to  take  the  place  of 
want  of  care  in  handling  manure  ;  they  should  be  used 
onh'  wdien  the  manure  receives  the  best  of  care. 

196.  Manure  Produced  in  Covered  Sheds  and  Box 
Stalls.  —  Manure  produced  under  cover  as  in  sheds 
and  box  stalls  is  of  superior  quality  to  that  produced 
in  any  other  way.  Losses  by  leaching  are  avoided, 
the  manure  is  compacted  by  the  tramping  of  animals, 
and  the  solid  and  liquid  excrements  are  more  evenly 
mixed  with  the  absorbents.  By  no  other  system  is 
there  such  a  large  percentage  of  the  fertility  recovered. 
Manure  from  w^ell-fed  cattle,  when  collected  and  pre- 
pared in  a  covered  shed,  will  have  about  the  follow- 
ing composition  : 

Per  cent. 

Water 70.00 

Nitrogen 0.90 

Phosphoric  acid 0.60 

Potash 0.70 

197.  Value  of  Protected  Manure.  —  Manure  that 
is  produced  under  cover  has  greater  crop-produ- 
cing powers  than  manure  that  is  cared  for  in  any  other 
way.  Experiments  by  Kinnard  show  that  such  ma- 
nure produced  4  tons  more  potatoes  per  acre  than  pile 
manure,  while  11  bushels  more  of  wheat  per  acre 
were  obtained  from  land  which  had  the  previous  year 


THE    USE    OF    MANURE  163 

received  the  covered  manure  than  from  land  which 
received  the  uncovered  manure. ^^ 

THE  USE  OF  MANURE 

198.  Direct  Hauling  to  Fields. —  It  is  always  desir- 
able, whenever  conditions  allow,  to  draw  the  manure 
directly  to  the  field  and  spread  it,  rather  than  to  allow 
it  to  accumulate  about  barns  or  in  the  barnyard. 
When  taken  directly  to  the  field  from  the  stable  no 
losses  by  leaching  occur,  and  the  slight  loss  from 
fermentation  and  volatilization  of  the  ammonia  are 
more  than  compensated  for  by  the  benefits  derived 
from  the  action  of  the  fresh  manure  upon  the  soil. 
When  manure  undergoes  fermentation  in  the  soil,  as 
previously  stated  it  combines  with  the  mineral  matter 
of  the  soil  and  produces  humates.  The  practice  of 
hauling  the  manure  directly  to  the  field  as  soon  as 
produced  is  the  most  economical  way  of  caring  for  it. 

With  scant  rainfall,  composting  the  manure  before 
spreading  is  necessary,  but  with  a  liberal  rainfall  it  is 
not  essential.  On  a  loam  soil  a  direct  application 
of  stable  manure  is  more  advisable  than  on  heavy  clay 
or  light  sandy  soils.  On  sandy  soils  there  is  frequently 
an  insufficient  supply  of  water  to  properly  ferment  the 
manure.  Manure  sometimes  fails  to  show  any  benefi- 
cial effects  the  first  year  on  heavy  cla)'  land,  because 
of  the  slow  rate  of  decomposition,  but  the  second  and 
third  years  the  beneficial  effects  are  noticeable. 


164 


SOILS    AND    FERTILIZERS 


199.  Coarse  Manure  May  Be  Injurious.  — The  ap- 
plication of  coarse  leached  manure  may  cause  the  soil 
to  be  SO  open  and  porous  as  to  affect  the  water  supply 
of  the  crop,  b)'  introducing,  below  the  surface  soil,  a 
layer  of  straw,  which  breaks  the  capillary  connection 
with  the  subsoil.  Coarse  manure  and  shallow  spring 
plowing  are  frequently  injurious,  when  fine  or  w^ell- 
composted  manure  and  fall  plowing  are  beneficial. 
The  injury  resulting  from  the  use  of  coarse  manure  is 
frequently  due  to  its  being  allowed  to  leach  before  it  is 
used,  so  that  it  does  not  properly  ferment  in  the  soil. 

200.  Manuring  Pasture  Land.  —  In  semiarid 
regions,  where  manure  decomposes  slowly,  it  is  some- 
times advisable  to  spread  it  upon  the  pasture   land  as 


IMlUIUxiiiUilliliiL 


Fig.  27.     Manured  land. 

a  top  dressing.  The  manure  encourages  the  growth 
of  grass,  which  appropriates  plant  food  otherwise  lost, 
and  it  also  acts  as  a  mulch  preventing  excessive  evapo- 
ration. Then  when  the  pasture  land  is  plowed  and  pre- 
pared for  a  grain  crop  it  contains  a  better  store  of  both 


THE    USE    OF    MANURE 


l6^ 


water  and  available  plant  food.     The    manuring    of 
pasture  lands  is  one   of  the  best  ways  of  utilizing  the 


Fig.  28.     Unmanured  land. 

manure  when  trouble  arises  from  slow  decomposition. 

201.  Small     Manure    Piles    Undesirable.  —  It   is 

sometimes  the  custom  to  make  a  large  number  of 
small  manure  piles  in  fields.  This  is  a  poor  practice, 
for  it  entails  additional  expense  in  spreading  the  ma- 
nure, and  the  small  piles  are  usually  so  constructed 
that  heavy  losses  occur,  and  the  manure,  when  finally 
spread,  is  not  uniform  in  composition.  Oats  grown  on 
land  manured  in  this  way  present  an  uneven  appear- 
ance. There  are  small  patches  of  thrifty,  overfed 
oats,  corresponding  to  the  places  occupied  by  the 
former  manure  piles,  while  large  areas  of  half-starv^ed 
oats  may  be  observed. 

202.  Rate  of  Application. —  The  amount  of  manure 
that  should  be  applied  depends  upon  the  nature  of  the 
soil  and  the  crop.  On  loam  soils  intended  for  general 
truck  purposes  heavier  applications  may  be  made  than 
when  grain  is  raised.     For  general  farm  purposes,  10 


l66  SOILS   AND    FERTILIZERS 

tons  per  acre  are  usually  sufficient.  It  is  better 
economy  to  make  frequent  light  applications  than 
heavier  ones  at  long  intervals.  When  manure  is 
spread  frequently  the  soil  is  kept  in  a  more  even  state 
of  fertility,  and  losses  by  percolation,  denitrification, 
and  ammonification  are  prevented. 

For  growing  garden  crops  20  tons  and  more  per  acre 
are  sometimes  used.  It  is  better,  however,  not  to  use 
stable  manure  too  liberally  for  trucking,  but  to  supple- 
ment it  with  special  fertilizers  as  the  crop  may  require. 
Soils  which  contain  a  large  amount  of  calcium  car- 
bonate admit  of  more  frequent  and  heavier  applications 
of  manure  than  soils  which  are  deficient  in  this  com- 
pound.    The  lime  aids  fermentation  and  nitrification. 

203.  Crops  Most  Suitable  for  Manuring. —  Soils 
which  contain  a  low  stock  of  fertility  will  admit  of 
manuring  for  the  production  of  almost  any  crop. 
Soils  well  stocked  with  plant  food,  like  some  of  the 
western  prairie  soils,  which  are  in  need  of  manure 
mainly  for  the  physical  action,  will  not  admit  of  its 
direct  use  on  all  crops.  On  a  prairie  soil  of  average 
fertility  an  application  of  well-rotted  manure  will 
cause  wheat  to  lodge.  When  it  cannot  be  applied  di- 
rectly to  a  crop,  it  may  be  used  indirectly.  It  never 
injures  corn  by  causing  too  rank  a  growth,  and  when 
wheat  follows  corn  which  has  been  manured  there  is 
but  little  danger  of  loss  from  lodging. 


THE   USE    OF    MANURE  1 67 

On  some  soils  stable  manure  cannot  be  used  for 
growing  sugar-beets ;  on  other  soils  it  does  not  seem  to 
exercise  an  injurious  effect.  Tobacco  is  injured  as  to 
quality  by  manure.  Crops,  as  flax,  tobacco,  sugar- 
beets,  and  wheat,  which  do  not  admit  of  direct  applica- 
tions of  stable  manure  all  require  the  manuring  of 
preceding  crops.  When  in  doubt  as  to  w^hat  crop  to 
apply  the  manure  to,  it  is  always  safe  to  apply  it  to  corn, 
and  then  to  follow  with  the  crop  which  would  have 
been  injured  by  its  direct  application. 

The  fact  that  coarse,  leached  manure  may  cause 
trouble  in  a  dry  season,  and  that  well-rotted  manure 
may  cause  grain  to  lodge,  are  no  substantial  reasons 
why  manure  should  be  wasted  as  it  frequently  is  in 
western  farming  by  being  burned,  used  for  making 
roads,  thrown  away  in  streams,  or  used  for  filling  up 
low  places. 

204.  Comparative  Value  of  Manure  and  Crops. — 

The  manure  from  a  given  amount  of  grain  or  fodder 
always  gives  better  results  than  if  the  food  itself  were 
used  directly  as  manure.  The  manure  from  a  ton  of 
bran  will  give  better  returns  than  if  the  bran  itself 
were  used.  This  is  because  so  little  of  the  fertilizing 
elements  is  extracted  in  the  process  of  digestion  and 
the  action  of  the  digestive  fluids  upon  the  food  makes 
the  manure  more  readily  available  as  a  fertilizer  than 
the  food  which  has  not  passed  through  any  of  the 
stages  of  fermentation.     It   is  better  economy  to  use 


l68  SOILS    AND    FERTILIZERS 

products  as  linseed  meal  and  cottonseed  meal  for  feed- 
ing stock,  and  take  good  care  of  the  manure,  than  to 
use  the  materials  directly. 

205.  Lasting  Effects  of  Manure.  —  No  other  ma- 
nures make  themselves  felt  for  so  long  a  time  as  farm 
manures.  In  ordinary  farm  practice  an  application  of 
stable  manure  will  visibly  affect  the  crops  for  a  num- 
ber of  years.  At  the  Rothamsted  Experiment  Station, 
records  have  been  kept  for  over  fifty  years  as  to  the 
effects  of  manures  upon  soils.  In  one  experiment 
manure  was  used  for  twenty  years  and  then  discon- 
tinued for  the  same  period.  It  was  observed  that 
when  its  use  was  discontinued  there  was  a  gradual  de- 
cline in  crop-producing  power,  but  not  so  rapid  as  on 
plots  where  no  manure  had  been  used.  The  manure 
which  had  been  applied  for  the  twenty-year  period 
prior  to  its  disuse  made  itself  felt  for  an  ensuing 
period  of  twenty  years. 

206.  Comparative  Value  of  Manure  Produced  on 
Two  Farms.  —  The  fact  that  there  is  a  great  differ- 
ence in  the  composition  and  value  of  manures  pro- 
duced on  different  farms  may  be  observed  from  the 
following  examples : 

On  one  farm  10  tons  of  timothy  are  fed.  The 
liquid  manure  is  not  preserved  and  25  per  cent,  of  the 
remaining  fertility  is  leached  out  of  the  solids,  while 
5  per  cent,  of  the  nitrogen  is  lost  by  volatilization. 
It  is  estimated  that  half  of  the  nitrogen  and  potash  of 


THE   USE    OF    MANURE 


169 


the  food  is  voided  in  the  urine.  On  account  of  the 
scant  amount  and  poor  quality  of  the  food  no  milk  or 
flesh  is  produced. 

On  another  farm  7.5  tons  of  clover  hay  and  2.5  tons 
of  bran  are  fed.     The  liquid  excrements  are  collected 


Fig.  29.     Good  manure. 


Fig.  30.     Poor  manure. 


and  the  manure  is  taken  directly  to  the  field  and 
spread.  It  is  estimated  that  20  per  cent,  of  the  nitro- 
gen and  4  per  cent,  of  the  phosphoric  acid  and  potash 
are  utilized  for  the  production  of  flesh  or  milk. 

The   relative    value  of   the  manures  from  the   two 
farms  is  as  follows : 


Farm  No.  i. 


In  10  tons  timothy, 
Lbs. 


Nitrogen 250 

Phosphoric  acid 90 

Potash 400 


Loss  in  urine. 


250  -7-  2  =:  125  lbs.  nitrogen 
400  -T-  2  =  200  lbs.  potash 


IJO  SOILS   AND    FERTILIZERS 

Loss  by  leaching. 
125  X  0.30  =  37.50  lbs.  nitrogen 
90  X  0-25  =  22.50  lbs.  phosphoric  acid 
200  X  0.25  =  50  lbs.  potash 

Total  loss. 
Lbs.  Per  cent. 

Nitrogen 162.5  65 

Phosphoric  acid 22.5  25 

Potash 250.0  62 

Present  in  final  product, 

manure  from  i  ton  timothy. 

Lbs. 

"Nitrogen 8,75 

Phosphoric  acid 6.75 

Potash 15.00 

Relative  money  value |;i.oo 

Farm  No.  2. 

In  10  tons  mixed  feed. 
Lbs. 

Nitrogen 400 

Phosphoric  acid 240 

Potash 300 

Loss,  sold  in  milk  and  retained  in  body. 
Lbs.  Per  cent. 

Nitrogen,  400X0.20 80  20 

Phosphoric  acid,  estimated 10  4 

Potash 12  4 

Present  in  final  product, 
manure  from  i  ton  feed. 

Lbs. 

Nitrogen 32.0 

Phosphoric  acid 23.0 

Potash 26.0 

Relative  money  value l'3-8o 

207.  Summary  of  Ways  in  which  Stable  Manure 
May  Be  Beneficial.  — 

I.   By  adding  new  stores  of  plant  food  to  the  soil. 


THE   USE    OF    MANURE  171 

2.  By  acting  upon  the  soil,  forming  huniates  and 
rendering  the  inert  plant  food  of  the  soil  more  availa- 
ble. 

3.  By  raising  the  temperature  of  the  soil. 

4.  By  making  the  soil  darker  colored. 

5.  By  enabling  soils  to  retain  more  water  and  to 
give  it  up  gradually  to  growing  crops. 

6.  By  improving  the  physical  condition  of  sandy 
and  clay  soils. 

7.  By  preventing  the  denuding  effects  of  heavy 
wind  storms. 


CHAPTER  VII 


PHOSPHATE  FERTILIZERS 

208.  Importance  of  Phosphorus  as  Plant  Food. — 

Phosphorus  in  the  form  of  phosphates  is  one  of  the 
essential  elements  of  plant  food.  None  of  the  higher 
orders  of  plants  can  complete  their 
growth  unless  supplied  with  this 
element  in  some  form.  The  illus- 
tration (Fig.  31)  shows  an  oat  plant 
which  received  no  phosphates,  but 
was  supplied  with  all  of  the  other 
elements  of  plant  food.  As  soon  as 
the  phosphates  stored  up  in  the 
seed  had  been  utilized,  the  plant 
ceased  to  grow,  and  after  a  few 
weeks  died  of  phosphate  starvation, 
having  made  the  total  growth 
shown  in  the  illustration.  All  crops 
demand  their  phosphates  at  an  early 
stage  in  their  development.  Wheat 
takes  up  eighty  per  cent,  of  its 
phosphoric  acid  in  the  first  half  of 
without  phosphorus.  ^\^q  growing  period,36  while  clover 
has  assimilated  all  of  its  phosphoric  acid  by  the 
time  the   plant  reaches  full  bloom. '^^     Phosphates  ac- 


Oat  plant  grown 


PHOSPHATE    FERTILIZERS  173 

cumulate,  to  a  great  extent,  in  the  seeds  of  all  grains 
and  are  usually  sold  from  the  farm,  especially  when 
grain  farming  is  extensively  followed.  All  crops  are 
very  sensitive  to  the  absence  of  phosphates;  an  imper- 
fect supply  results  in  the  production  of  light  weight 
grains.  The  nitrogen  and  the  phosphates  are  to  a 
great  extent  stored  up  in  the  same  parts  of  the  plant, 
particularly  in  the  seed,  which  is  richer  in  both 
nitrogen  and  phosphorus  than  is  any  other  part. 
Nitrogen  is  the  chief  element  of  protein,  while  phos- 
phorus is  necessary  to  aid  in  transporting  the  pro- 
tein compounds  through  the  cell  walls  of  plants. 
In  speaking  of  the  phosphorus  in  plants  and  in  fer- 
tilizers, as  well  as  in  soils,  the  term  phosphoric  acid 
or  phosphoric  anhydride  is  used.  This  is  because 
phosphorus  is  an  acid-forming  element  and,  as  already 
explained,  the  anhydride  of  the  element  is  always  con- 
sidered instead  of  the  element  itself. 

209.  Amount  of  Phosphoric  Acid  Removed  in 
Crops. — The  amount  of  phosphoric  acid  removed 
in  an  acre  of  different  farm  crops  ranges  from  1 8  to  30 
pounds : 

Phosphoric  acid 
per  acre. 

Lbs. 

Wheat,  20  bu 12.5 

Straw,  2,000  lbs 7.5 

Total 20.0 


174  SOILS   AND    FERTILIZERS 

Phosphoric  acid 
per  acre. 

Lbs. 

Barley,  40  bu 15 

Straw,  3,000  lbs 5 

Total 20 

Oats,  50  bu 12 

Straw,  3,000  lbs 6 

Total 18 

Corn,  65  bu 18 

Stalks,  4,000  lbs 4 

Total 22 

Peas,  3,500  lbs 25 

Red  clover,  4,000  lbs < 28 

Potatoes,   150  bu 20 

Flax,  15  bu 15 

Straw,  1,800  lbs 3 

Total 18 

210.  Amount  of  Phosphoric  Acid  in  Soils.  —  To 

meet  the  demand  of  growing  crops  (for  25  pounds  of 
phosphoric  acid  per  acre),  there  is  present  in  soils  from 
1,000,  and  less,  to  8,000  pounds  of  phosphoric  acid  per 
acre,  of  which,  however,  only  a  fraction  is  available  as 
plant  food  at  any  one  time.  The  availability  of  phos- 
phoric acid  is  a  factor  which  has  a  great  deal  to  do  in 
determining  crop-producing  power.  INIany  soils  contain 
a  large  amount  of  total  phosphoric  acid,  which  has  be- 
come unavailable  because  of  poor  cultivation  and  the 


PHOSPHATE    FERTILIZERS  I  75 

absence  of  stable  manure  and  lime  to  combine  with 
the  phosphates  and  render  them  available. 

211.  Source   of   Phosphoric   Acid  in  Soils. —  The 

phosphates  fonnd  in  soils  are  derived  mainh'  from  the 
disintegration  of  phosphate  rock,  and  from  the  remains 
of  animal  life.  The  phosphate  deposits  fonnd  in  various 
localities  are  supposed  to  have  been  derived  either 
from  the  remains  of  marine  animals  or  from  sea-water 
highly  charged  with  soluble  phosphates.  These  de- 
posits have  been  subjected  to  various  geological  and 
climatic  changes  which  have  resulted  in  the  formation 
of  soft  phosphate,  pebble  phosphate,  and  rock  phos- 
phate.^^ 

212.  Commercial  Forms  of  Phosphoric  Acid. —  The 
commercial  sources  of  phosphate  fertilizers  are  (i) 
phosphate  rock,  (2)  bones  and  bone  preparations,  (3) 
phosphate  slag,  and  (4)  guano.  With  the  exception 
of  phosphate  slag  and  guano,  the  prevailing  form  of 
the  phosphorus  is  tricalcium  phosphate.  Before  be- 
ing used  for  commercial  purposes,  the  tricalcium 
phosphate,  which  is  insoluble  and  unavailable,  is 
treated  with  sulphuric  acid  which  produces  monocal- 
cium  phosphate,  a  soluble  and  available  form  of  plant 
food. 

Ca^CPO^X  +  2H,SO^  +  sno  =  CaH/PO;,  ^  HO  + 

2CaS0  .2H  O. 

4  2 

In  making  phosphate   fertilizers  from  bones  or  phos- 


176  SOILS   AND    FERTILIZERS 

pliate  rock  an  excess  of  the  rock  is  used  so  that  there 
will  be  no  free  acid  to  be  injurious  to  vegetation. 

213.  Different    Forms  of   Calcium    Phosphate. — 

The  usual  form  in  which  calcium  phosphate  is  found 
in  nature  is  tricalcium  phosphate,  Ca  (PO  )^.  Unless 
associated  with  organic  matter  or  salts  which  render 
it  soluble  it  is  of  but  little  value  as  plant  food.  When 
tricalcium  phosphate  is  treated  with  sulphuric  acid, 
monocalcium  phosphate,  CaH  (PO  )^,  is  formed.  This 
compound  is  soluble  in  water  and  directly  available  as 
plant  food.  When  tricalcium  and  monocalcium  phos- 
phate are  brought  together  in  a  moist  condition,  di- 
calcium  phosphate  is  produced. 

Ca  (PO  )   +  CaH  (PO  )   =  2Ca  H  (PO  ) . 

3\  4'2      '  4N  4/2  2       2\  4/2 

Another  form  of  phosphate  of  lime,  met  with  in  basic 
phosphate  slag,  is  tetracalcium  phosphate,  (CaO)  P^O.. 

214.  Reverted  Phosphoric  Acid.  — When  mono- 
and  tricalcium  phosphate  react,  the  product  is  known 
as  reverted  phosphoric  acid,  which  is  insoluble  in 
water,  but  is  not  in  such  form  as  to  be  unavailable  as 
plant  food.  It  is  generally  considered  that  the  re- 
verted phosphoric  acid  is  available  as  plant  food  :  it  is 
soluble  in  a  dilute  solution  of  ammonium  citrate,  and 
is  sometimes  spoken  of  as  citrate-soluble  phosphoric 
acid.  Citrate-soluble  phosphoric  acid  may  also  be 
formed  by  the  action  upon  the  monocalcium  phos- 
phate of   iron   and  aluminum   compounds  present  as 


PHOSPHATE    FERTILIZERS  I  77 

impurities  in  the  phosphate  rock.  This  process  is  a 
fixation  change,  as  described  in  Chapter  V.  In  an  old 
fertilizer  there  may  be  present  citrate-soluble  phos- 
phoric acid  in  two  forms,  as  dicalcium  phosphate  and 
as  hydrated  phosphates  of  iron  and  aluminum.  The 
citrate-soluble  phosphoric  acid  in  fertilizers  is  not  all 
equally  valuable  as  plant  food  because  of  the  different 
phosphate  compounds  that  may  be  dissolved. 

215.  Available  Phosphoric  Acid.  —  As  applied  to 
fertilizers,  the  term  available  phosphoric  acid  includes 
the  water-soluble  and  citrate-soluble  phosphoric  acid. 
These  solvents  do  not,  under  all  conditions,  make  a 
sharp  distinction  as  to  the  available  and  unavailable 
phosphoric  acid  when  it  comes  to  plant  grow^th.  Some 
forms  of  bones,  w^hich  are  insoluble  in  an  ammonium 
citrate  solution  are  available  as  plant  food,  and  then 
again  some  forms  of  aluminum  phosphate  w^hich  are 
soluble  are  of  but  little  value  as  plant  food.  The 
terms  available  and  unavailable  phosphoric  acid,  as 
applied  to  commercial  fertilizers,  refer  to  the  solubility 
of  the  phosphates,  and  as  a  general  rule  their  value  as 
plant  food  is  in  accord  w4th  their  solubilities.  The 
more  insoluble  the  less  valuable  the  material. 

216.  Phosphate  Rock.  —  Phosphate  rock  is  found 
in  many  parts  of  the  United  States,  particularly  in 
South  Carolina,  North  Carolina,  Florida,  Virginia, 
and  Tennessee.  The  deposits  occur  in  stratified 
veins,  as  well  as  in  beds  and  pockets.     There  are  dif- 


1 78  SOILS   AND    FERTILIZERS 

ferent  types  of  phosphates  as  hard  rock,  soft  rock,  land 
pebble,  and  river  pebble.  The  pebble  phosphates  are 
found  either  on  land  or  collected  in  cavities  in  the 
water  courses,  and  are  generally  spherical  masses  of 
variable  size.  The  soft  rock  phosphate  is  easily 
crushed,  while  the  hard  rock  requires  pulverizing  with 
rock  crushers.  Phosphate  rock  usually  contains  from 
40  to  70  per  cent,  of  calcium  phosphate,  the  equiva- 
lent of  from  17  to  30  per  cent,  phosphoric  acid.  The 
remaining  30  to  60  per  cent,  is  composed  of  fine  sand, 
limestone,  alumina  and  iron  compounds,  with  other 
impurities,  which  often  render  a  phosphate  unsuitable 
for  manufacturing  high-grade  fertilizer.  Raw  phos- 
phate rock  is  usually  sold  at  the  mines  for  #1.75  to 
$4.50  per  ton. 

217.  Superphosphate. — Pulverized  rock  phosphate 
known  as  phosphate  flour,  is  treated  with  commercial 
sulphuric  acid  and  soluble  monocalcium  phosphate 
obtained.  The  amount  of  sulphuric  acid  used  is  de- 
termined from  the  composition  of  the  rock.  Impuri- 
ties as  calcium  carbonate  and  calciinn  fluoride  react 
with  sulphuric  acid  and  caUvSe  a  loss  of  acid.  Ordi- 
narily, a  ton  of  high-grade  phosphate  rock  requires  a 
ton  of  sulphuric  acid.  The  mixing  is  usually  done  in 
lead-lined  tanks.  A  weighed  amount  of  phosphate 
flour  is  placed  in  the  tank,  and  the  sulphuric  acid 
added,  through  lead  pipes,  from  the  acid  tower.  The 
mixing  of  the  acid  and  phosphate  is  done  with  a  me- 


PHOSPHATE    FERTILIZERS  179 

chanical  mixer,  driven  by  machiner}-.  From  the 
mixer  the  material  is  passed  into  large  tanks,  where 
two  or  three  days  are  allowed  for  the  completion  of 
the  reaction.  When  the  mass  solidifies,  it  is  ground 
and  sold  as  superphosphate.  In  the  manufacture  of 
superphosphate,  gypsum  (CaSO  .2H^0)  is  always  pro- 
duced. A  ton  of  superphosphate  prepared  from  high- 
grade  rock  in  the  way  outlined  will  contain  about  40 
per  cent,  of  lime  phosphates,  equivalent  to  1 8  per  cent, 
phosphoric  acid.  If  a  poorer  quality  of  rock  is  used  a 
proportionally  smaller  amount  of  phosphoric  acid  is 
obtained.  A  more  concentrated  superphosphate  is  ob- 
tained b}'  producing  phosphoric  acid  from  the  phos- 
phate rock,  and  then  allowing  the  phosphoric  acid  to 
act  upon  fresh  portions  of  the  rock,  the  reactions  be- 
ing as  follows  :^3 


Ca^CPO^X  +  3H,S0^  =  3CaS0,  -  2H^(P0;, 
C^iJiPOX  +  4^P0^  ^  3HP  =  3[CaH  (POJ^.H  O]. 
Ca/PO^X  +  aH  P0^  +  i2H  O  =  3[Ca  H,(PO;,.4H  O]. 

The  phosphoric  acid  is  separated  from  the  gypsum  be- 
fore acting  upon  the  phosphate  flour.  In  this  way, 
superphosphate  containing  from  35  to  45  per  cent, 
of  phosphoric  acid  is  produced.  When  fertilizers  are 
to  be  transported  long  distances  this  concentrated  prod- 
uct is  preferable.  The  terms  'acid'  and  'superphosphate' 
are  generally  used  to  designate  both  the  first  product 
formed  by  the  action   of  sulphuric  acid  and  that  pro- 


l8o  SOILS   AND    FERTILIZERS 

duced  by  the  phosphoric  acid  but  of  late  there  is  a  ten- 
dency to  restrict  the  term  'acid  phosphate'  to  the 
product  formed  by  the  action  of  sulphuric  acid,  and 
the  term  'super-phosphate'  to  the  concentrated  product 
formed  by  the  action  of  phosphoric  acid. 

218.  Commercial  Value  of  Phosphoric  Acid. —  The 
commercial  value  of  phosphoric  acid  in  fertilizers  is 
determined  by  the  value  of  the  crude  phosphate  rock, 
cost  of  grinding  and  treating  with  sulphuric  acid,  and 
cost  of  transportation.  The  price  of  phosphoric  acid 
in  superphosphates  usually  ranges  from  5  to  6  cents 
per  pound.  The  field  value,  that  is  the  increased 
yields  obtained  from  the  use  of  superphosphates,  may 
not  be  in  accord  with  the  commercial  value  because  so 
many  conditions  govern  its  use.  The  phosphoric  acid 
obtained  from  feed-stuffs  is  usually  considered  worth 
about  a  cent  a  pound  less  than  that  from  superphos- 
phates. Water-soluble  phosphoric  acid  is  generally 
rated  a  half  cent  per  pound  higher  than  citrate-soluble 
phosphoric  acid. 

219.  Phosphate  Slag.  —  In  the  refining  of  iron  ores 
by  the  Bessemer  process,  the  phosphorus  in  the  iron  is 
removed  as  a  basic  slag.  The  lime,  which  is  used  as  a 
flux,  melts  and  combines  with  the  phosphorus  of  the 
ore,  forming  phosphate  of  lime.  The  slag  has  a  varia- 
ble composition.  The  process  by  \vhich  the  phos- 
phorus of  pig  iron  is  removed  and  converted  into  basic 
phosphate  slag  is  known  as  the  Thomas  process,  and 


PHOSPHATE    FERTILIZERS  l8l 

the  product  is  sometimes  called  Thomas'  slag.  At  the 
present  time  but  little  basic  slag  is  produced  for  fer- 
tilizer purposes  in  this  country.  In  Germany  and 
some  other  European  countries  the  amount  used  is 
nearly  equal  to  the  amount  of  superphosphate.  Phos- 
phate slag  is  ground  to  a  fine  powder  and  is  applied 
directly  to  the  land,  without  undergoing  the  sulphuric 
acid  treatment.  Phosphoric  acid  is  present  mainly  in 
the  form  of  tetracalcium  phosphate,  (CaO)  P^O.. 

220.  Guano  is  the  Spanish  for  dung,  and  is  a  concen- 
trated form  of  nitrogenous  and  phosphate  manure  of 
interest  mainly  on  account  of  its  historic  significance. 
It  is  a  mixture  of  sea-fowl  droppings  which  have  ac- 
cumulated along  the  seacoast  in  sheltered  regions. 
The  mixture  of  dung,  dead  animals,  and  debris,  has 
undergone  fermentation,  and  is  concentrated  in  both 
nitrogen  and  phosphoric  acid.  The  introduction  of 
guano  into  Europe  marked  an  important  period  in  agri- 
culture, inasmuch  as  its  use  demonstrated  the  action 
and  importance  of  concentrated  fertilizers.  All  of  the 
best  beds  of  guano  have  been  exhausted  and  only  a 
little  of  the  poorer  grades  are  now  found  on  the  mar- 
ket. The  best  qualities  of  guano  contained  from  12 
to  15  per  cent,  of  phosphoric  acid,  10  to  12  per  cent, 
of  nitrogen,  and  from  5  to  7  per  cent,  of  alkaline  salts. 

BONE  FERTILIZERS 

221.  Raw  Bones  contain,  in  addition  to  phosphate 
of  lime,  Ca  (PO  )  ,  org^anic  matter  which  makes  them 

'  3^  4'2'  o 


162  SOILS   AND    FERTILIZERS 

slow  in  decomposing  and  slow  in  their  action  as  a  fer- 
tilizer. Before  being  used  as  fertilizer  they  should  be  fer- 
mented in  a  compost  heap  with  wood  ashes  in  the  fol- 
lowing way :  A  protected  place  is  selected  so  that  no 
losses  from  drainage  will  occur.  A  layer  of  well-com- 
pacted manure  is  covered  with  wood  ashes,  the  bones 
are  then  added  and  well  covered  with  manure  and 
wood  ashes.  From  three  to  six  months  should  be  al- 
lowed for  the  bones  to  ferment.  The  large,  coarse 
pieces  may  then  be  crushed  and  are  ready  for  use. 
The  presence  of  fatty  material  in  a  fertilizer  retards  its 
action  because  fat  is  so  slow  in  decomposing.  Bones 
from  which  the  organic  matter  has  been  removed  are 
more  active  as  a  fertilizer  than  raw  bones.  Bones 
contain  from  i8  to  25  per  cent,  of  phosphoric  acid  and 
from  2  to  4  per  cent,  of  nitrogen.  The  amount  and 
value  of  the  citrate-soluble  phosphoric  acid  in  bones 
are  extremely  variable. 

222.  Bone  Ash  is  the  product  obtained  when  bones 
are  burned.  It  is  not  extensively  used  as  a  fertilizer 
because  of  the  greater  commercial  value  of  bone-black. 
It  contains  about  36  per  cent,  of  phosphoric  acid,  and 
is  more  concentrated  than  raw  bones. 

223.  Steamed  Bones.  —  Raw  bones  are  subjected  to 
superheated  steam  to  remove  the  fat  and  ossean  which 
are  used  for  making  soap  and  glue;  they  are  then  pul- 
verized and  sold  as  fertilizer  imder  the  name  of  bone 
meal,  which  contains  from  1.5  to  2.5  per  cent,  of  nitro- 


BONE    FERTILIZERS  183 

gen  and  from  22  to  29  per  cent,  of  phosphoric  acid. 
Steamed  bones  make  a  more  active  fertilizer  than  raw 
bones.  Occasionally,  well-prepared  bone  meal  is  used 
for  feeding  pigs  and  fattening  stock  in  the  same  way 
that  flesh  meal  is  used. 

224.  Dissolved  Bone.  —  When  bones  are  treated 
with  sulphuric  acid  as  in  the  manufacture  of  super- 
phosphates the  product  is  called  dissolved  bone.  The 
tricalcium  phosphate  undergoes  a  change  to  more 
available  forms,  as  described,  and  the  nitrogen  is  ren- 
dered more  available.  Dissolved  bone  contains  from 
2  to  3  per  cent,  of  nitrogen  and  from  15  to  17  per 
cent,  of  phosphoric  acid. 

225.  Bone-black.  — When  bones  are  distilled  bone- 
black  is  obtained.  It  is  extensively  employed  for  re- 
fining sugar,  and  after  it  has  been  used  and  lost  its 
power  of  decolorizing  solutions,  it  is  sold  as  fertilizer. 
It  contains  about  30  per  cent,  phosphoric  acid  and  is  a 
concentrated  phosphate  fertilizer. 

226.  Use  of  Phosphate  Fertilizers.  —  The  amount 
of  phosphoric  acid  advisable  to  apph'  to  crops,  varies 
with  the  nature  of  the  soil  and  the  kind  of  crop  to  be  pro- 
duced. On  a  poor  soil  400  pounds  of  superphosphate 
per  acre  is  an  average  application.  It  is  usually  ap- 
plied as  a  top  dressing  just  before  seeding,  and  may  be 
placed  near  the  hills  of  corn  or  potatoes,  but  not  in 
contact  with  the  seed.  It  is  not  advisable  to  make 
heavy  applications  of  superphosphates  at  long  inter- 


184  SOILS   AND    FERTILIZERS 

vals,  because  the  process  of  fixation  ma}-  take  place  to 
such  an  extent  that  crops  are  unable  to  utilize  the  fer- 
tilizer. Lighter  and  more  frequent  applications  are 
preferable.  Phosphates  should  not  be  mixed  with 
lime  carbonate  or  with  loam  before  spreading.^'  It  is 
best  to  apply  the  fertilizer  directly  to  the  land.  Phos- 
phates may  be  used  in  connection  with  farm  manures. 
Many  soils  which  contain  liberal  amounts  of  total 
phosphoric  acid  are  improved  with  a  light  dressing  of 
superphosphates.  Such  soils,  however,  should  be  more 
thoroughly  cultivated,  and  manured  with  farm  ma- 
nures, to  make  the  phosphates  available.  There  is 
frequently  an  apparent  lack  of  phosphoric  acid  in  the 
soil  when  in  reality  the  trouble  is  due  to  other  causes, 
as  lack  of  organic  matter  to  combine  with  the  phos- 
phates or  to  a  deficiency  of  lime.  Before  using  phos- 
phate fertilizers,  careful  field  tests  should  be  made  to 
determine  if  the  soil  is  in  actual  need  of  available 
phosphoric  acid.  Directions  for  making  these  tests 
are  given  in  Chapter  X. 

227.  How  to  Keep  the  Phosphoric  Acid  Available. 

—  Phosphoric  acid  associated  with  organic  matter  in 
a  moderately  alkaline  soil,  is  more  available  than  that 
in  acid  soils.  Soft  phosphate  rock  may  be  mixed  with 
manure  or  materials  like  cottonseed  meal  and  made 
slowly  available  for  crops.  Soils  which  have  a  good 
stock  of  phosphoric  acid,  when  kept  well  manured, 
and    occasionallv    limed    if    necessarv,  contain  a    lib- 


BONE    FERTILIZERS  185 

eral  supply  of  available  phosphoric  acid.  As  an  illus- 
tration, the  following  example  of  two  soils  from  ad- 
joining farms,  which  have  been  cropped  and  manured 
differently,  may  be  cited  :^° 

Soil  well  manured  No  manure  and 

and  crops  continuous  wheat 

rotated.  raising. 

Per  cent.  Per  cent. 
Total  phosphoric  acid  ••• .  0.20  0.20 

Humus 4.25  1.62 

Humic  phosphoric  acid  . .  0.06  0.02 

It  is  more  economical  to  keep  the  insoluble  phos- 
phoric acid  of  the  soil  in  available  forms  by  the  use  of 
farm  manures  than  it  is  to  purchase  superphosphates. 


CHAPTER  VIII 


POTASH  FERTILIZERS 

228.  Potassium   an   Essential  Element   of   Plant 
Food.  —  Potassium  is  one  of  the  three  elements  most 

essential  as  plant  food.  When  it  is 
removed  from  a  soil  plants  are  un- 
able to  develop.  Oats  seeded  in  a 
soil  from  which  the  potash  only 
had  been  extracted  made  the  total 
growth  shown  in  the  illustration 
(Fig.  32).  When  potash  is  present 
in  the  soil  in  liberal  amounts  vig- 
orous plants  are  produced.  Potash, 
like  phosphoric  acid  and  nitrogen, 
is  utilized  by  crops  in  the  early 
stages  of  growth.  Potassium  does 
not  accumulate  in  seeds  to  the  same 
extent  as  phosphoric  acid  and  nitro- 
gen, but  is  present  mainly  in  stems 
and  leaves,  consequently  when 
straw  crops  are  utilized  in  pro- 
grown  without  potash,  ducing  manure  the  potash  is  not 
lost  or  sold  from  the  farm.  But  with  ordinary  grain 
farming  excessive  losses  of  potash  do  occur,  particu- 
larly when  the  straw  is  burned  and  the  ashes  are  wasted. 


Fig.  32.     Oat  plant 


POTASH    FERTILIZERS  187 

229.  Amount  of  Potash  Removed  in  Crops.  —  In 

grain  crops  from  35  to  60  pounds  of  potash  per  acre 
are  removed  from  the  soil.  For  grass  crops  more  pot- 
ash is  required  than  for  grains,  while  roots  and  tubers 
require  more  than  grass.  The  approximate  amount  of 
potash  removed  in  various  crops  is  given  in  the  fol- 
lowing table  :37 

Potash  per  acre. 
Ivbs. 

Wheat,  20  bu 7 

Straw,  2,000  lbs 28 

Total 35 

Barley,  40  bu 8 

Straw,  3,000  lbs 30 

Total 38 

Oats,  50  bu 10 

Straw,  3,000  lbs 35 

Total 45 

Corn,  65  bu 15 

Stalks,  3.000  lbs 45 

Total 60 

Peas,  30  bu 22 

Straw,  3,500  lbs 38 

Total 60 

Flax,  15  bu 19 

Straw,  1 ,800  lbs 8 

Total 27 


l88  SOILS   AND    FERTILIZERS 

Mangels,  lo  tons 150 

Meadow  hay,  i  ton 45 

Clover  hay,  2  tons •    •  66 

Potatoes,  150  bushels 75 

230.  Amount  of  Potash  in  Soils.  —  In  ordinary 
soils  there  are  from  3,500  to  12,000  pounds  of  potash 
per  acre  to  the  depth  of  one  foot.  Many  soils  with 
apparently  a  good  stock  of  total  potash  give  excellent 
results  when  a  light  dressing  of  potash  salts  is  applied. 
The  amount  of  available  potash  in  the  soil  is  more 
difficult  to  estimate  than  the  available  phosphoric 
acid.  There  is  also  a  great  difference  in  crops  as  to 
their  power  of  obtaining  potash.  Some  require 
greater  help  in  procuring  this  element  than  others.  A 
lack  of  available  potash  is  sometimes  indirectly  due  to 
a  deficiency  of  other  alkaline  matter  in  the  soil,  which 
prevents  the  necessary  changes  taking  place  in  order 
that  the  potash  may  be  liberated  as  plant  food. 

231.  Sources  of  Potash  in  Soils.  —  The  main 
source  of  the  soil  potash  is  feldspar,  which,  after  dis- 
integration, is  broken  up  into  kaolin  and  potash  com- 
pounds. Mica  and  granite  also,  in  some  localities, 
contribute  liberal  amounts.  The  most  valuable  forms 
of  potash  are  the  zeolitic  silicates.  The  amount  of 
water-soluble  potash,  except  in  alkaline  soils,  is  ex- 
tremely small.  By  the  action  of  many  fertilizers  the 
potash  compounds  undergo  changes  in  composition. 
For  example,  the  gypsum  which  is  always  present  in 


STASSFURT   SALTS  1 89 

acid  phosphates,  liberates  some  potash.  The  potash 
compounds  of  the  soil  are  in  various  degrees  of  com- 
plexity from  forms  soluble  in  dilute  acids  to  insoluble 
minerals  as  feldspar. 

232.  Commercial  Forms  of  Potash.  —  Prior  to  the 
introduction  of  the  Stassfurt  salts,  wood  ashes  were 
the  main  source  of  potash.  Since  the  discovery  and 
development  of  the  Stassfurt  mines,  the  natural  prod- 
ucts as  kainit,  and  muriate  and  sulphate  of  potash  have 
been  extensively  used  for  fertilizing  purposes.  A 
small  amount  of  potash  is  also  obtained  from  waste 
products  as  tobacco  stems,  cottonseed  hulls,  and  the 
refuse  from  beet-sugar  factories. 

STASSFURT  SALTS 

233.  Occurrence. ^3 —  I'he  Stassfurt  mines  were  first 
worked  with  the  view  of  procuring  rock  salt.  The 
presence  of  the  various  compounds  of  potash,  soda,  and 
magnesia,  associated  with  the  layers  of  rock  salt,  were 
regarded  as  troublesome  impurities,  and  attempts  were 
made  by  sinking  new  shafts  to  avoid  them,  but  with 
the  result  of  finding  them  in  greater  abundance. 
About  1864  their  value  as  potash  fertilizers  was  es- 
tablished. The  mines  are  now  owned  and  worked  by 
a  syndicate.  It  is  supposed  that  at  one  time  the 
region  about  the  mines  was  submerged  and  filled  with 
sea-water.  The  tropical  climate  of  that  geological  period 
caused  rapid  evaporation,  which  resulted  in  forming 
mineral  deposits,  the  less  soluble  material  as  lime  sul- 


190  SOILS   AND    FERTILIZERS 

phate  being  first  deposited,  then  a  layer  of  rock  salt, 
and  finally  layers  of  potash  and  magnesium  salts  in 
the  order  of  their  solubility. 

234.  Kainit  is  a  mineral  composed  of  potassium 
sulphate,  magnesium  sulphate,  magnesium  chloride, 
and  water  of  cr}'stallization.  As  it  comes  from  the 
mine  it  is  mixed  with  gypsum,  salt,  potassium  chlo- 
ride, and  other  bodies.  Kainit  contains  from  1 2  to  1 2. 50 
per  cent,  of  potash,  and  is  one  of  the  most  important 
of  the  Stassfurt  salts.  It  is  extensively  used  as  a  pot- 
ash fertilizer,  and  is  also  mixed  with  other  materials 
and  sold  as  a  commercial  fertilizer.  The  magnesium 
chloride  causes  it  to  absorb  water,  and  the  presence  of 
other  compounds  results  in  the  formation  of  hard 
lumps,  whenever  kainit  is  kept  for  a  long  time. 
Kainit  is  soluble  in  water,  and  can  be  -  used  as  a  top 
dressing  at  the  rate  of  75  to  200  pounds  or  more  per  acre. 

235.  Sulphate  of  Potash.  —  High-grade  sulphate 
of  potash  is  prepared  from  some  of  the  crude  Stassfurt 
salts,  and  may  contain  as  high  as  97  per  cent.  K^SO  . 
Low-grade  sulphate  of  potash  is  about  90  per  cent, 
pure.  High-grade  sulphate  of  potash  contains  about 
50  per  cent,  of  potassium  oxide  (K^O),  and  is  one  of 
the  most  concentrated  forms  of  potash  fertilizer.  It 
is  particularly  valuable  because  it  can  be  safely  used  on 
crops  as  tobacco  and  potatoes  which  would  be  injured 
in  quality  if  muriate  of  potash  were  applied,  or  if 
much  chlorine  were  present. 


STASSFURT   SALTS  191 

236.  Miscellaneous  Potash  Salts. — Carnallit,  9 
per  cent.  K^,  — composed  of  KCl.MgC1^.6Hp. 
Polyhalit,  15  per  cent.  K^O, — composed  of  K^SO  .Mg 
SO^.(CaSOJ^.Hp.  Krugit,  10  per  cent.  K^,— com- 
posed of  K^s6^.MgS0^.(CaS0J^.Hp.  Sylvinit,  16 
to  20  per  cent.  K^O, — composed  of  KCl.NaCl  and 
impurities.  Kieserit,  7  per  cent.  K^O,  — composed  of 
MgSO  and  carnallit. 

237.  Wood  Ashes.  —  For  ordinary  agricultural  pur- 
poses, wood  ashes  are  the  most  important  source  of 
potash.  Ashes  are  exceedingly  variable  in  composi- 
tion. When  leached  the  soluble  salts  are  extracted 
and  there  is  left  only  about  i  per  cent,  of  potash.  In 
unleached  ashes  the  amount  of  potash  ranges  from  2 
to  10  per  cent.  Soft  wood  ashes  contain  much  less 
potash  than  hard  wood  ashes.  Goessmann  gives  the 
following  as  the  average  of  97  samples  of  ashes  :^^ 

Average  composition.  Range. 

Per  cent.  Per  cent. 

Potash 5.5  2.5  to  10.2 

Pho.sphoric  acid 1.9  0.3  to    4.0 

Lime 34.3  18.0  to  50.9 

In  10,000  pounds  of  wood.  Potash.  Phosphoric  acid. 

Lbs.  Lbs. 

White  oak 10.6  2.5 

Red  oak 14.0  6.0 

Ash 15.0  I.I 

Pine 0.8  0.7 

Georgia  pine 5.0  1,2 

Dogwood 9.0  5.7 


192  SOILS    AND    FERTILIZERS 

238.  Action  of  Ashes  on  Soils.  —  In  ashes,  the  pot- 
ash is  present  mainly  as  potassinni  carbonate.  Ashes 
are  nsnally  regarded  as  a  potash  fertilizer  only,  but 
they  also  contain  lime  and  phosphoric  acid,  and  may 
be  very  beneficial  in  supplying  these  elements.  They 
are  valuable  too  because  they  add  alkaline  matter  to 
the  soil,  which  corrects  acidity  and  aids  nitrification. 
A  dressing  of  ashes  improves  the  mechanical  condi- 
tion of  many  soils  by  binding  together  the  soil  parti- 
cles. This  property  is  well  illustrated  in  the  so-called 
"Gumbo"  soils,  which  contain  so  much  alkaline  mat- 
ter that  the  soil  has  a  soapy  taste  and  feel,  and  when 
plowed  the  particles  fail  to  separate. 

239.  Leached  Ashes.  —  When  ashes  are  leached  the 
soluble  salts  are  extracted,  and  the  insoluble  matter 
which  is  left  is  composed  mainly  of  calciinn  carbonate 
and  silica. ^5 

Uuleached  ashes.  Leached  ashes. 

Per  cent.  Per  cent. 

Water 12.0  30.0 

Silica,  etc 13.0  13.0 

Potassium  carbonate 5.5  i.i 

Calciiuii              "          61.0  51.0 

Phosphoric  acid 1.9  1.4 

240.  Alkalinity  of  Leached  and  Unleached  Ashes. 

—  A  g^ood  wav  to  detect  leached  ashes  is  to  deter- 
mine  the  alkalinity  in  the  following  way  :  Weigh 
out  2  grams  of  ashes  into  a  beaker,  add  100  cc.  dis- 
tilled water,  and  heat  on  a  sand-bath  nearly  to  boiling, 


STASSFURT    SALTS  I93 

cool,  and  filter.  To  50  cc.  of  the  filtrate  add  about  3 
drops  of  cochineal  indicator,  and  then  a  standard  solu- 
tion of  hydrochloric  acid  from  a  burette  until  the  solu- 
tion is  neutral.  If  a  standard  solution  of  acid  cannot 
be  procured,  one  containing  15  cc.  concentrated  hydro- 
chloric acid  per  liter  of  distilled  water  may  be  used  for 
comparative  purposes.  Leached  ashes  require  less  than 
2  cc.  of  acid  to  neutralize  the  alkaline  matter  in  i  gram 
while  unleached  ashes  require  from  10  to  i8cc.  In  pur- 
chasing wood  ashes,  if  a  chemical  analysis  cannot  be 
secured,  the  alkalinity  of  the  ash  should  be  determined. 

241.  Coal  and  Other  Ashes.  — Since  the  amount  of 
phosphoric  acid  and  potash  in  coal  ashes  is  very  small, 
they  have  but  little  fertilizer  value.  Soft-coal  ashes  con- 
tain more  potash  than  those  from  hard  coal,  but  it  is  held 
in  such  forms  of  combination  as  to  be  of  but  little  value. 

The  ashes  from  sawmills  where  soft  wood  is  burned 
and  the  ashes  are  unprotected,  are  nearly  worthless. 
When  peat-bogs  are  burned  over,  large  amounts  of  ashes 
are  produced.  If  the  bogs  are  covered  with  timber, 
the  ashes  are  sometimes  of  sufiicient  value  to  warrant 
their  transportation  and  use. 

Phosphoric 
Potash.  acid. 

Per  cent.  Per  cent. 

Hard  coal o.  10  o.  10 

Soft  coal 0.40  0.40 

Sawmill  ashes'^ 1.20  i.oo 

Peat-bog  ashes'^ 1.15  0.54 

Peat-bog  ashes  (timbered)'^  3.68  2.56 

Tobacco  stems 4.00  7.00 

Cottonseed  hulls 20.00  7.00 


194  SOILS   AND    FERTILIZERS 

242.  Commercial  Value  of  Potash.  —  The  market 
value  of  potash  is  determined  from  the  selling  price  of 
high-grade  sulphate  of  potash  and  kainit.  Ordinarily, 
the  price  per  pound  of  potash  varies  from  4  to  5  cents. 
As  in  the  case  of  both  nitrogen  and  phosphoric  acid, 
the  market  and  the  field  values  may  be  entirely  at 
variance.  Before  potash  salts  are  used,  careful  field 
tests  should  be  made  to  determine  the  actual  condi- 
tion of  the  soil  as  to  its  needs  in  potash. 

243.  Use  of  Potash  Fertilizers.  —  Wood  ashes,  or 
Stassfurt  salts,  should  not  be  used  in  excessive 
amounts.  Not  more  than  300  pounds  per  acre  should 
be  applied  unless  the  soil  is  known  to  be  markedly  de- 
ficient, and  previous  tests  indicate  that  larger  amounts 
are  safe  and  advisable.  Potash  fertilizers  should  be 
evenly  spread  and  not  allowed  to  come  in  contact  with 
plant  tissue.  They  should  be  used  early  in  the  spring 
before  seeding  or  before  the  crop  has  made  much 
growth.  Wood  ashes  make  an  excellent  top  dressing 
for  grass  lands,  particularly  where  it  is  desired  to  en- 
courage the  growth  of  clover.  There  are  but  few 
crops  or  soils  that  are  not  greatly  benefited  by  a  light 
application  of  wood  ashes,  and  none  should  ever  be 
allowed  to  leach  or  waste  about  a  fann. 

When  a  potash  fertilizer  is  used,  a  dressing  of  lime 
will  frequently  be  beneficial.  The  potash  undergoes 
fixation,  and  when  it  is  liberated  there  should  be  some 
basic  material  as  lime  to  take  its  place.     Goessmann 


STASSFURT   SALTS  I95 

obsen-ed  that  land  manured  for  several  years  with 
potassium  chloride  finally  produced  sickly  crops,  but 
that  an  application  of  slaked  lime  restored  a  healthy 
appearance  to  succeeding  crops. ^^  If  the  soil  is  well 
stocked  with  lime  its  joint  use  with  potash  fertilizers 
is  not  necessar}'. 


CHAPTER  IX 


LIME  AND  MISCELLANEOUS  FERTILIZERS 

244.  Calcium  an  Essential  Element  of  Plant  Food. 

—  Calcium  is  present  in  the  ash  of  all  plants,   and  is 
usually  more  abundant   in   soils   than   phosphorus  or 

potassium.  It  takes  an  essential 
part  in  plant  growth,  and  when- 
ever withheld  grow^th  is  checked. 
The  effect  of  removing  calcium 
from  the  soil  is  shown  in  the  illus- 
tration (Fig.  1,^,)^  wdiich  gives  the 
total  growth  made  by  an  oat  plant 
under  such  a  condition. 

Plants  grown  on  soils  deficient 
in  calcium  compounds,  lack  hard- 
iness. They  are  not  so  able  to 
withstand  drought,  or  climatic 
changes,  as  plants  grown  on  soils 
well  supplied  wath  this  element. 
Calcium  does  not  accumulate 
in  the  seeds  of  plants,  but  is  pres- 
ent mainly  in  the  leaves  and 
stems  where  it  takes  an  impor- 
tant part  in  the  production  of  new 
tissue.  The  term  lime  is  used  in 
speaking  of  the  calcium  oxide  content  of  soils  and  crops. 


>'ig-  33- 
Oat  plant  grown  with- 
out lime. 


LIME    AND    MIvSCELLANEOUS    FERTILIZERS  197 

245.  Amount  of  Lime  Removed  in  Crops. ^^  — 

Pounds  per  acre. 

Wheat,  20  bushels i 

Straw,  2000  pounds 7 

Total 8 

Corn,  65  bushels i 

Stalks,  3000  pounds 11 

Total 12 

Peas,  30  bushels 4 

Straw,  3500  pounds 71 

Total 75 

Flax,  15  bushels ' 3 

Straw,  1800  pounds 13 

Total 16 

Clover,  4000  pounds 75 

Clover  and  peas  remove  so  much  lime  from  the  soil 
that  they  are  often  called  lime  plants.  The  amount 
required  by  grain  and  hay  is  small  compared  with  that 
required  for  a  clover  or  pea  crop. 

246.  Amount  of  Lime  in  Soils.  —  There  is  no  ele- 
ment in  the  soil  in  such  variable  amounts  as  calcium. 
It  may  be  present  from  a  few  hundredths  of  a  per  cent, 
to  twenty  per  cent.;  soils  which  contain  from  0.4  to 
0.5  per  cent,  are  usually  well  supplied.  The  lime  in 
a  soil  takes  an  important  part  in  soil  fertility ;  when 
deficient,  humic  acid  may  be  formed,  nitrification 
checked, and  the  soil  particles  will  lack  binding  material. 


198  SOILS   AND    FERTILIZERS 

247.  Different  Kinds  of  Lime  Fertilizers.  — By  the 

term  'lime  fertilizer'  is  usually  meant  land  plaster 
(CaSO  .2IIO).  Occasionally  quicklime  (CaO)  and 
slaked  lime  (Ca(OH)^)  are  used  on  exceedingly  sour 
land.  In  general  a  lime  fertilizer  is  one  which  sup- 
plies the  element  calcium ;  common  usage,  however, 
has  restricted  the  term  to  sulphate  of  lime. 

248.  Action  of  Lime  Fertilizers  upon  Soils.  —  Lime 
fertilizers  act  both  chemically  and  physically.  Chem- 
ically, lime  unites  with  the  organic  matter  to  form 
humate  of  lime  and  prevent  the  formation  of  humic 
acid.  It  aids  in  nitrification  and  acts  upon  the  soil, 
liberating  potassium  and  other  elements  of  plant  food. 
Physically,  lime  improves  capillarity,  precipitates  clay 
when  suspended  in  water,  and  prevents  losses,  as  the 
washing  away  of  fine  earth. 

249.  Action  of  Lime  upon  Organic  Matter.  — When 
soils  are  deficient  in  lime,  an  acid  condition  may  de- 
velop to  such  an  extent  as  to  be  injurious  to  vegeta- 
tion. In  fact  nitrogen,  phosphoric  acid,  and  potash 
may  all  be  present  in  liberal  amounts,  but  in  the 
absence  of  lime  poor  results  will  be  obtained.  Ex- 
periments at  the  Rhode  Island  Experiment  Station 
indicate  that  there  are  large  areas  of  acid  soils  in  the 
Eastern  States  which  are  much  improved  when  treated 
with  air-slaked  lime.^^  There  is  a  great  difference  in 
the  power  of  plants  to  live  in  acid  soils.  Agricultural 
plants  are  particularly  sensitive,   while  many  weeds 


LIME    AND    MISCELLANEOUS    FERTILIZERS         1 99 

have  such  strong  power  of  endurance  that  they  are 
able  to  thrive  in  the  presence  of  acids.  The  charac- 
ter of  the  weeds  frequently  reflects  the  character  of  the 
soil  as  to  acidity,  in  the  same  way  that  an  "alkali" 
soil  is  indicated  by  the  plants  produced. 

250.  Lime  Liberates  Potash.  —  The  action  of  lime 
upon  soils  well  stocked  with  potash  results  in  the  fixa- 
tion of  the  lime  and  the  liberation  of  the  potash  ;  the 
reaction  takes  place  in  accord  with  the  well-known 
exchange  of  bases.  The  extent  to  which  potash  may 
be  liberated  by  lime  depends  upon  the  firmness  with 
which  the  potash  is  held  in  the  soil.  Boussingault 
found  that  when  clover  was  limed  there  was  present 
in  the  crop  three  times  as  much  potash  as  in  a  similar 
crop  not  limed.     His  results  are  as  follows :  ^^ 

Kilos  per  hectare. 
In  crop  not  limed.  In  limed  crop. 

First  Second  First  Second 

year.  year.  year.  year. 

Lime 32.2  32.2  79.4  102.8 

Potash  26.7  28.6  95.6  97.2 

Phosphoric  acid,   ii.o  7.0  24.2  22.9 

The  indirect  action  of  land  plaster  upon  Western 
prairie  soils  in  liberating  plant  food,  particularly 
potash  and  phosphoric  acid,  is  unusually  marked. 
Laboratory  experiments  show^  that  small  amounts  of 
gypsum  are  quite  active  in  rendering  potash,  phos- 
phoric acid,  and  even  nitrogen  soluble  in  the  soil 
water.  5 


200  SOILS   AND    FERTILIZERS 

251.  Quicklime  and  Slaked  Lime.  —  When  it  is  de- 
sired to  correct  acidity  slaked  lime  is  used.  Air- 
slaked  lime  is  not  as  valuable  as  water-slaked  lime. 
Quicklime  cannot  be  used  on  land  after  a  crop  has 
been  seeded.  Both  slaked  lime  and  quicklime 
should  be  applied  some  little  time  before  seed- 
ing and  not  to  the  crops.  The  action  of  quicklime 
upon  organic  matter  is  so  rapid  that  it  destroys  vege- 
tation.    Slaked  lime  is  less  injurious  to  vegetation. 

252.  Pulverized  Lime  Rock.  —  In  some  localities 
pulverized  lime  rock  is  used.  It  may  be  applied  as  a 
top-dressing  in  almost  unlimited  amounts.  It  is  most 
beneficial  on  light,  sandy  soils,  where  it  performs  the 
function  of  fine  clay  as  well  as  being  beneficial  in  its 
chemical  action.  Not  all  soils  are  alike  responsive  to 
applications  of  limestone,  and  before  using,  it  is  best 
to  determine  to  what  extent  it  will  be  beneficial. 
There  are  no  conditions  where  limestone  is  injurious 
to  soil  or  crop. 

253.  Marl. — Underlying  beds  of  peat,  deposits  of 
marl  are  occasionally  found.  Marl  is  a  mixture  of 
disintegrated  limestone  and  clay,  and  contains  varia- 
ble amounts  of  calcium  carbonate,  phosphoric  acid, 
and  potash.  When  peat  and  marl  are  found  together 
they  may  be  used  jointly  with  manure  as  described  in 
Section  175.  Many  sandy  lands  in  the  vicinity  of  peat 
and  marl  deposits  would  be  greatly  improved,  both 
physically  and  chemically,  by  the  use  of  these  materials. 


LIME    AND    MISCELLANEOUS    FERTILIZERS         20I 

254.  Physical  Action  of  Lime. — The  addition  of 
lime  fertilizers  to  sandy  soils  improves  their  general 
physical  condition.  Heavy  clays  lose  their  plasticity 
when  limed ;  the  fine  clay  particles  are  cemented 
and  act  as  sand,  which  improves  the  mechanical 
condition  of  the  soil.  The  physical  action  of  lime 
upon  soils  is  well  illUvStrated  in  the  case  of  'loess  soils,' 
which  are  composed  of  clay  and  limestone.  The 
lime  cements  the  clay  particles  and  forms  compound 
grains,  making  the  soil  more  permeable,  and  more 
easily  tilled.  The  improved  physical  condition  alone 
which  follows  the  application  of  lime  fertilizers,  is  fre- 
quently sufficient  to  warrant  their  use. 

255.  Application  of  Lime  Fertilizers.  —  Lime  is 
generally  used  as  a  top-dressing  on  grass  lands  at  the 
rate  of  200  to  500  pounds  per  acre.  Excessive  appli- 
cations are  undesirable.  Lime  as  gypsum  is  particu- 
larly valuable  when  applied  to  land  where  crops  are 
grown  which  assimilate  large  amounts  of  lime.  It 
should  be  remembered  that  it  is  not  a  complete,  but 
mainly  an  indirect,  fertilizer. 

If  used  to  excess  it  may  get  the  soil  in  such  a  con- 
dition that  no  more  plant  food  can  be  rendered  avail- 
able. A  common  saying  is  "  Lime  makes  the  father 
rich  but  the  son  poor.""  This  is  true,  however,  only 
when  lime  is  used  in  excess.  When  used  occasion- 
ally in  connection  with  other  manures,  it  has  no  inju- 
rious effects    upon   the  soil  and  is   a  valuable  fertil- 


202  SOILS   AND    FERTILIZERS 

izer,  especially  where  clover  is  grown  w4th  difficulty. 
MISCELLANEOUS  FERTILIZERS 

256.  Salt  is  frequently  used  as  an  indirect  fertilizer. 
Sodium  and  chlorine,  the  two  elements  of  which  it  is 
composed,  are  not  absolutely  necessary  for  normal 
plant  growth.  When  salt  is  applied  to  the  soil  and 
the  sodium  undergoes  fixation,  potassium  may  be 
liberated.  An  early  experiment  of  Wolff  illustrates 
this  point :  a  buckwheat  plot  fertilized  with  salt  pro- 
duced a  crop  with  more  potash  and  less  sodium  than 
a  similar  unfertilized  plot. 

Salt  may  be  used  to  check  the  rank  grow^th  of  straw 
during  a  rainy  season,  and  thus  prevent  loss  of  the 
crop  by  lodging.  It  should  not  be  used  in  excessive 
amounts,  as  it  is  destructive  to  vegetation ;  200  pounds 
per  acre  is  a  fair  application.  Salt  also  improves  the 
physical  condition  of  the  soil  by  increasing  the  surface- 
tension  of  the  soil  water.  Salt  should  not  be  used  on 
a  tobacco  or  potato  crop,  because  it  injures  the  quality 
of  the  product. 

257.  Magnesium  Salts. —  Magnesium  is  present  in 
the  ash  of  all  plants,  and  is  an  essential  element  of 
plant  growth.  Usually  soils  are  so  well  stocked  with 
this  element  that  it  is  not  necessary  to  apply  it  in 
fertilizers.  Some  of  the  magnesium  salts,  as  the 
chloride,  are  injurious  to  vegetation,  but  when  associa- 
ted with  lime  as  carbonate,  magnesia  imparts  fertility. 
In  many  of  the  Stassfurt  salts  magnesium  is  present. 


MISCELLANEOUS   FERTILIZERS  203 

258.  Soot. — The  deposits  formed  in  boilers  and 
chimneys  when  wood  and  soft  coal  are  burned  contain 
small  amounts -of  potash  and  phosphoric  acid.  They 
are  valuable  mainly  as  mechanical  fertilizers  impart- 
ing the  properties  of  organic  matter.  There  is  but 
little  plant  food  in  soot,  as  shown  by  the  following 
analysis : 

Soft-coal  soot.  Hard-wood  soot. 

Per  cent. 13  Per  ceut.69 

Potash     0.84  1.78 

Phosphoric  acid 0.75  0.96 

259.  Seaweeds.  —  Seaweeds  are  rich  in  potash 
and  near  the  sea  coast  are  extensively  used  for  fer- 
tilizers. 

Composition  of 

mixed   seaweed. 

Per  cent  ^9 

Water 81 .50 

Nitrogen 0.73 

Potash 1.50 

Phosphoric  acid o.  18 

260.  Strand  Plant  Ash.  —  Weeds  and  plants  pro- 
duced on  waste  land  along  the  sea  are  in  many  Euro- 
pean countries  burned,  and  the  ashes  used  as  fertilizer 
on  other  lands.  By  this  means  waste  land  is  made  to 
produce  fertilizer  for  fields  which  are  tillable.  The 
amount  of  fertility  removed  in  weeds  is  usually  greater 
than  that  in  agricultural  plants,  because  weeds  have  a 
greater  power  of  obtaining  food  from  the  soil.  When 
wheat  or  other  grain  is  raised,  and  a  small  crop  of 
grain  and  a  large  crop  of  weeds  are  the  result,  there 
is  more  fertility  removed  from  the  soil  than  if  a  heavy 


204  SOILS    AND    FERTILIZERS 

stand  of  grain  were  obtained.  The  ashes  of  strand 
plants  and  weeds  are  extremely  variable  in  composition. 
261.  Wool  Washings  and  Waste. — The  washings 
from  wool  contain  snfficient  potash  to  make  this 
material  vahiable  as  a  fertilizer.  In  wool  there  is  a 
high  per  cent,  of  potash,  which  is  soluble,  and  readily 
removed  in  the  w^ashings.  Wool  waste  may  contain 
from  I  to  5  per  cent,  of  potash  and  from  4  to  7  per 
cent,  of  nitroeen  in  somewhat  inert  forms. 


CHAPTER  X 


COMMERCIAL  FERTILIZERS  AND  THEIR  USE 

262.  Development  of  the  Commercial  Fertilizer 
Industry.  —  The  commercial  fertilizer  industry  owes 
its  origin  to  Liebig's  work  on  plant  ash.  The  first 
superphosphate  was  made  by  Sir  J.  B.  Lawes,  about 
1840,  from  spent  bone-black  and  sulphuric  acid.  His 
interest  had  previously  been  attracted  to  the  use  of 
bones  by  a  gentleman  who  farmed  near  him,  "  who 
pointed  out  that  on  one  farm  bone  was  invaluable  for 
the  turnip  crop,  and  on  another  farm  it  was  useless.  "^^ 
Since  i860  the  commercial  fertilizer  industry  in  this 
country  has  developed  rapidly,  until  now  the  amount 
of  money  expended  in  purchasing  commercial  fer- 
tilizers and  amendments  is  estimated  at  $60,000,000 
annually.  Nearly  all  of  this  sum  is  expended  in  less 
than  a  quarter  of  the  area  of  the  United  States. 

263.  Complete  Fertilizers  and  Amendments.  — The 

term  commercial  fertilizer  is  applied  to  those  materials 
which  are  made  by  the  mixing  of  different  substances 
which  contain  plant  food  in  concentrated  forms. 
When  a  commercial  fertilizer  contains  nitrogen,  phos- 
phoric acid,  and  potash,  it  is  called  a  complete  fer- 
tilizer, because  it  supplies  the  three  elements  which  are 
liable  to  be  most  deficient.    Materials  as  sodium  nitrate 


2o6  SOILS   AND    FERTILIZERS 

which  supply  only  one  element  are  called  amend- 
ments. It  frequently  happens  that  a  vSoil  requires  only 
one  element  in  order  to  produce  good  crops.  In  such 
cases  only  the  one  element  needed  should  be  sup- 
plied. Complete  fertilizers  are  sometimes  used  when 
the  soil  is  only  in  need  of  an  amendment. 

264.  Variable  Composition  of  Commercial  Fer- 
tilizers.—  Since  commercial  fertilizers  are  made  by 
mixing  various  materials  which  contain  different 
amounts  of  nitrogen,  phosphoric  acid,  and  potash,  it 
follows  that  they  are  extremely  variable  in  composi- 
tion and  value.  No  two  samples  are  the  same, 
hence  the  importance  of  knowing  the  com- 
position of  every  separate  brand  purchased.  The 
composition  of  fertilizers  is  varied  to  meet  the  require- 
ments of  different  soils  and  crops.  Some  fertilizers 
are  made  rich  in  phosphoric  acid,  while  others  are 
rich  in  nitrogen  and  potash. 

265.  How  a  Fertilizer  is  Made.  —  The  most  com- 
mon materials  used  in  making  complete  fertilizers 
are  :  Nitrate  of  soda,  kainit,  and  dissolved  phosphate 
rock.  These  materials  have  about  the  following  com- 
position : 

Nitrate  of  soda 15.5  per  cent,  nitrogen. 

Kainit 12.5  per  cent,  potash. 

Dissolved  phosphate .  •  •    14.0  per  cent,  phosphoric  acid. 

The  fertilizer  may  be  made  rich  or  poor  in  any  one 
element.     Many    fertilizers    contain    about    twice    as 


COMMERCIAL    FERTILIZERS  209 

example  could  be  made  from  feldspar  rock,  apatite 
rock,  and  leather.  The  leather  contains  nitrogen, 
the  apatite  contains  phosphoric  acid,  and  the  feldspar, 
potash.  Such  a  fertilizer  would  have  no  value  when 
used  on  a  crop,  because  all  of  the  plant  food  elements 
are  present  in  unavailable  forms.  Hence,  in  purchas- 
ing fertilizers,  it  is  necessary  to  know  not  only  the 
percentage  composition,  but  also  the  nature  of  the 
materials  from  which  the  fertilizer  was  made. 

267.  Inspection  of  Fertilizers. — In  many  states 
laws  have  been  enacted  regulating  the  manufacture 
and  sale  of  commercial  fertilizers,  and  provision  is  made 
for  inspection  and  analysis  of  all  brands  offered  for 
sale.  The  label  on  the  fertilizer  package  must  specify 
the  percentage  amounts  of  nitrogen,  available  phos- 
phoric acid  and  potash.  Inspection  has  been  found 
necessary  in  order  to  protect  the  farmer  and  the  honest 
manufacturer. 

Occasionally  a  fraud  is  revealed  like  the  following  :  7° 

Natural  plant  food  $25  to  I28  per  ton. 
Composition,  Per  cent. 

Total  phosphoric  acid 22.21 

Insoluble     "  "    20.81 

Available     "  "    1.40 

Potash  soluble  in  water o.  13 

Actual  value  per  ton,  $1.52. 

268.  Mechanical  Condition  of  Fertilizers. — When 
a  fertilizer  is  purchased,  the  mechanical  condition 
should     also    be    considered.       The     finer     the    fer- 


2IO  SOILS    AND    FERTILIZERS 

tilizer,  as  a  rule,  the  better  it  is  for  promoting  crop 
growth.  Some  combinations  of  plant  food  produce 
fertilizers  which  become  so  hard  and  lumpy  that  it  is 
difficult  to  crush  the  lumps  before  spreading.  The 
mass  must  be  pulverized  so  as  to  be  evenly  distributed, 
otherwise  the  plant  food  will  not  be  economically 
used.  A  fertilizer  that  passes  through  a  sieve  with 
holes  0.25  mm.  in  diameter  is  more  valuable  and  can 
be  used  to  better  advantage  than  one  of  the  same  com- 
position that  requires  a  0.5  mm.  sieve. 

269.  Forms  of  Nitrogen  in  Commercial  Fertilizers. 

—  Nitrogen  is  present  in  commercial  fertilizers  in  three 
forms  :  (i)  /Vmmonium  salts,(2)  nitrates,  and  (3) organic 
nitrogen.  The  organic  nitrogen  is  divided  into  tw^o 
classes:  [a)  soluble  in  pepsin  solution,  and  (d)  insolu- 
ble in  pepsin  solution.  The  relative  values  of  these 
different  forms  of  nitrogen  are  discussed  in  Chapter 
IV.  Three  fertilizers  may  have  the  same  amount  of 
total  nitrogen  and  still  have  entirely  different  crop- 
producing  powers. 

.  No.  I.  No.  2.  No.  '^. 

Nitrogen  as  :  Per  cent.       Per  cent.       Per  cent. 

Ammonium  compounds    ...    1.75  0.25  o.  10 

Nitrates 0.15  0,15  o.  10 

Organic  nitrogen  : 

Soluble  in  pepsin o.  10  1.25  0.55 

Insoluble  in  pepsin 0.35  1.25 

Total 2.00  2.00  2.00 

In  purchasing  fertilizers  it  is  important  to  know  not 
only   the   amount  of   nitrogen,  but  also  the  form  in 


COMMERCIAL    FERTILIZERS  211 

which  it  is  present.  In  No.  3  the  nitrogen  is  in  inert 
forms  like  leather,  while  in  No.  2  it  is  largely  in  the 
form  of  dried  blood,  and  No.  i  has  mainly  ammonium 
compounds.  Each  of  these  fertilizers,  as  explained  in 
the  chapter  on  nitrogenous  manures,  has  a  different 
plant  food  value. 

270.  Phosphoric  Acid.  —  There  are  three  forms  of 
phosphoric  acid  in  commercial  fertilizers:  (i)  Water- 
soluble,  (2)  citrate-soluble,  and  (3)  insoluble.  The 
water-  and  citrate-soluble  are  called  the  available  phos- 
phoric acid.  In  most  fertilizers  the  phosphoric  acid  is 
derived  from  dissolved  phosphate  rock,  and  is  in  the 
form  of  monocalcium  phosphate.  The  citrate-soluble 
is  mainly  dicalcium  phosphate  with  variable  amounts 
of  iron  and  aluminum  phosphates  in  easily  soluble 
forms.  The  insoluble  phosphoric  acid  is  tricalcium 
and  other  phosphates  which  are  soluble  only  in  strong 
mineral  acids.  The  insoluble  phosphoric  acid  in  fer- 
tilizers is  considered  as  having  but  little  value.  As 
in  the  case  of  nitrogen  three  fertilizers  may  have  the 
same  total  amount  of  phosphoric  acid  and  yet  have 
entirely  different  values. 

Water-soluble  phosphoric  acid 
Citrate-soluble         "  " 

Insoluble 

Total 10.00  10.00  10.00 

No.  3  is  of  but  little  value;  the  fertilizer  contains  in- 


No.  I. 
;r  cent. 

No.  2. 
Per  cent. 

No.  3. 
Per  cent. 

8.00 

0.25 

0.25 

1.50 

8.00 

0.75 

0.50 

1-75 

9.00 

212  SOILS    AND    FERTILIZERS 

soluble  phosphate  rock  or  some  material  of  the  same 
nature.  No.  i  is  the  most  valuable,  because  it  con- 
tains the  least  insoluble  phosphoric  acid.  This  fer- 
tilizer contains  dissolved  phosphate  rock  or  dissolved 
bone.  No.  2  is  composed  of  such  materials  as  the  best 
grade  of  basic  slag  or  roasted  aluminum  phosphate 
or  fine  steamed  bone. 

271.  Potash.  —  The  three  forms  of  potash  in  fer- 
tilizers are:  (i)  water-soluble,  (2)  acid-soluble,  and  (3) 
insoluble.  Materials  as  sulphate  of  potash,  kainit,  and 
muriate  of  potash,  which  are  soluble  in  water,  be- 
long to  the  first  class.  In  some  states  the  fertilizer 
laws  recognize  only  the  water-soluble  potash.  In  the 
second  class  are  found  materials  like  tobacco  stems 
and  the  organic  forms  of  potash.  Substances  like 
feldspar,  which  contain  insoluble  potash,  are  of  no 
value  in  fertilizers.  As  a  rule,  the  potash  in  commer- 
cial fertilizers  is  soluble  in  water;  in  only  a  few  cases 
are  acid-soluble  forms  met  with.  Insoluble  potash 
would  be  considered  an  adulterant. 

272.  Misleading  Statements  on  Fertilizer  Pack- 
ages. —  Occasionally  the  percentage  amounts  of  nitro- 
gen, phosphoric  acid,  and  potash  are  stated  in  mis- 
leading ways  as  annnonia,  sulphate  of  potash,  and 
bone  phosphate  of  lime.  Inasmuch  as  14/17  of  am- 
monia is  nitrogen,  the  percentage  figure  for  ammonia 
is  proportionally  greater  than  the  nitrogen.  And  so 
with  sulphate  of  potash  which  contains  about  50  per 


COMMERCIAL    FERTILIZERS  213 

cent,  potash.  This  method  of  stating  the  composition 
can  be  considered  in  no  other  way  than  a  fraud, 
especially  when  the  fertilizer  contains  no  sulphate  of 
potash,  but  cheaper  materials,  and  the  phosphoric  acid 
is  not  derived  from  bone. 

273.  Estimated  Commercial  Value  of  Fertilizers, 

— The  estimated  value  of  a  commercial  fertilizer  is 
obtained  from  the  percentage  composition  and  the 
trade  value  of  the  materials  used.  Suppose  that  two 
fertilizers  are  selling  for  $25  and  $30,  respectively, 
each  having  a  different  composition,  the  estimated 
values  would  be  obtained  in  the  following  way  : 

Composition  of  Fertilizers. 

No.  I.  No.  2. 

Selling  ptice  $25.       Selling  price  $30, 

Percent.  Percent. 

Nitrogen  as  nitrates 1.50  2.10 

Pho.sphoric  acid,  available 8.00  lo.co 

"             "      insoluble 2.00  0.50 

Potash  ( water-soluble) 2.00  3.50 

Pounds  per  Ton. 

No.  I.  No.  2. 

Nitrogen 1.50  X  20  =    30  2. 10  X  20  ^=    42 

Phosphoric  acid  .   8.0    X  20  =  160  lo.o    X  20  =^  200 

Potash 2.0    X  20  ^    40  3.5    X  20  =    70 

Estimated  Value. 

No.  r.  No.  2. 

Nitrogen 30  X  o.  145  =  I4.35  42  X  o.  145  =  $6.09 

Phosphoric  acid 160  X  0.06    =    9.60  200  X  0.06    =  12.00 

Potash 40X0-045=^    i-8o  70X0.045=    3.15 

I15.75  121.24 


214 


SOILS    AND    FERTILIZERS 


Difference  between  estimated  value  and  selling 
price,  No.  i,  $9.25;  No.  2,  $8.76. 

274.  Home  Mixing. — At  the  New  Jersey  Experi- 
ment Station  it  has  been  shown  that  "  the  charges  of 
the  manufacturers  and  dealers  for  mixing,  bagging, 
shipping,  and  other  expenses  are  on  the  average  $8,50 
per  ton,  and  also  that  the  average  manufactured  fer- 
tilizer contains  about  300  pounds  of  actual  fertilizing 
constituents  per  ton.     These   figures   are    practically 


,>  ^ 


Fig.  34.  Composition  of  P'ertilizers. 


true  of  other  states  where  large  quantities  of  commer- 
cial fertilizers  are  used.'^^i  ii;^  states  where  smaller 
amounts  are  used  the  difference  between  the  estimated 
cost  and  selling  price  is  greater  than  $8.50. 

These  facts  emphasize  the  economy  of  home  mixing. 
The  difference  in  price  between  the  raw  materials 
and  the  product  sold  is  frequently  so  great  that  it  is  an 
advantage  for  the  farmer  to  purchase  the  raw  mate- 
rials, as  sulphate  of  potash,  nitrate  of  soda,  and  acid 


COMMERCIAL    FERTILIZERS  215 

phosphate,  and  mix  them  as  desired.  By  so  doing  a 
fertilizer  of  any  composition  may  be  prepared  and 
there  is  less  danger  of  securing  an  inferior  article. 
Of  course  it  is  not  possible  by  means  of  shovels  and 
sieves  to  accomplish  as  thorough  mixing  of  the  ingre- 
dients as   with   machiner^^ 


Formula  No.  i. 

Pounds. 

Nitrate  of  soda 500     containing  nitrogen  • . 

Acid  phosphate 1200     containing  phos.  acid 

Sulphate  of  potash  • .     300     containing  potash 150.0 


0 

Pounds. 

Percenta|;^e 

composition 

fertilizer. 

77-5 

3-87 

16S.0 

8.40 

150.0 

7.50 

Total 395.5 

Formula  No.  2, 

Nitrate  of  soda 250     containing  nitrogen 38.7       1.99 

Acid  phosphate 900     containing  phos.  acid-  •  126.0       6.3 

Sulphate  of  potash  . .     450     containing  potash 225.0     11. 5 

Plaster,  etc 400 


Total 389.7 

Formula  No.  3. 

Nitrate  of  soda 200     containing  nitrogen 31.0       1.55 

Acid  phosphate 1500     containing  phos.  acid..-    210.0     10.50 

Sulphate  of  potash  . .      150     containing  potash 75.0       5.75 

Plaster,  etc 150 


Total 316.0 

275.  Fertilizers  and  Tillage.  —  Commercial  fer- 
tilizers cannot  be  made  to  take  the  place  of  good 
tillage,  which  is  equally  as  important  when  fertilizers 


2l6  SOILS    AND    FERTILIZERS 

are  used  as  when  they  are  omitted.  Scant  crops  are 
as  frequently  due  to  the  want  of  proper  tillage  as  to 
the  absence  of  plant  food.  Poor  cultivation  results  in 
getting  the  soil  out  of  condition ;  then  instead  of  thor- 
oughly preparing  the  land,  commercial  fertilizers  are 
resorted  to,  and  the  conclusion  is  reached  that  the  soil 
is  exhausted,  when  in  reality  it  is  suffering  for  the  want 
of  cultivation,  for  a  dressing  of  land  plaster,  for  farm 
manures,  or  for  a  change  of  crops.  There  is  no  ques- 
tion but  what  better  tillage,  better  care  and  use  of 
farm  manures,  the  culture  of  clover  and  the  systematic 
rotation  of  crops  would  result  in  greatly  reducing  the 
$60,000,000  annually  spent  for  commercial  fertilizers, 
without  reducing  the  yield  of  crops.  The  better  the 
cultivation,  the  less  the  amount  of  commercial  fer- 
tilizer required. 

276,  Abuse  of  Commercial  Fertilizers. —  When  a 
soil  produces  poor  crops,  a  complete  fertilizer  is  fre- 
quently used  when  an  amendment  only  is  needed. 
Restricted  crop  production  in  long  cultivated  soils  is 
due  to  deficiency  of  available  nitrogen.  If  the  nitro- 
gen were  supplied,  improved  cultivation  would  gen- 
erally furnish  the  available  potash  and  phosphoric 
acid,  but  instead  of  providing  the  one  element  needed, 
others  which  may  already  be  present  in  the  soil  in 
liberal  amounts,  are  often  supplied  at  a  great  expense. 
Another  abuse  of  fertilizers  is  their  application  to  the 
wrong  crop.     A  heavy  application  of  potash  fertilizer 


FIELD   TESTS   WITH    FERTILIZERS  217 

to  a  wheat  crop  grown  on  a  clay  soil,  or  an  application 
of  nitrate  of  soda  on  land  seeded  to  clover,  or  of  land 
plaster  to  flax  grown  on  a  limestone  soil,  would  be  a 
useless  waste  of  money. 

277.  Proper  Use  of  Fertilizers.  — In  order  to  make 
the  best  use  of  commercial  fertilizers,  both  the  soil  and 
the  crop  must  be  carefully  considered.  All  crops  do 
not  possess  the  same  power  of  obtaining  food  from  the 
soil ;  turnips,  for  example,  have  very  restricted  powers 
of  phosphate  assimilation,  hence  they  require  special 
manuring  wdth  phosphates.  Wheat  requires  help  in 
obtaining  its  nitrogen.  A  wdieat  crop  will  starve  for 
the  want  of  nitrogen,  while  an  adjoining  corn  crop  will 
scarcely  feel  its  need.  Wheat  has  strong  power  of 
assimilating  potash  compounds,  while  clover  has  less. 
Hence  in  the  proper  use  of  fertilizers  the  power  of  the 
plant  to  obtain  its  food  must  be  considered.  An 
application  of  potash  to  clover,  nitrogen  to  wheat,  and 
phosphoric  acid  to  turnips,  would  be  a  judicious  use  of 
these  fertilizers,  while  if  a  mixture  of  the  three  ele- 
ments were  applied  to  each  crop  alike,  the  clover 
would  not  be  particularly  benefited  by  the  nitrogen 
or  the  wheat  by  the  potash.  Before  commercial  fertili- 
zers are  used,  careful  field  trials  should  be  made  with 
different  crops. 

FIELD  TESTS  WITH  FERTILIZERS 

278.  Experimental  Plots,  —  A  piece  of  land  w^ell 


2l8  SOILS    AND    FERTILIZERS 

tilled  and  of  uniform  texture,  should  be  used  for  field 
trials  with  fertilizers.  After  preparation  for  the  crop, 
small  plots,  1/20  of  an  acre,  are  staked  off.  A  con- 
venient size  is,  leiio;th  204  feet,  width  10  feet  8  inches, 
area  2176  square  feet.  Between  each  plot  a  strip  3 
feet  wide  should  be  left.  In  these  experiments  the 
plan  is  to  apply  one  element  or  a  combination  of 
elements  to  a  plot  and  compare  the  results  with  other 
plots  treated  differently.^^ 

279.  Preliminary  Trials.  —  It  is  best  to  make  pre- 
liminary trials  one  year  and  verify  the  conclusions  the 
next.  In  making-  the  tests  the  first  year  eight  plots 
are  necessary  and  fertilizers  are  applied  in  the  follow- 
ing way : 

The  first  plot  receives  no  fertilizer  and  is  used  as  the 
basis  for  comparison. 

The  second  plot  receives  a  dressing  of  8  pounds  of 
nitrate  of  soda,  16  pounds  acid  ]>hosphate,  and  8 
pounds  sulphate  or  muriate  of  potash. 

The  third  plot  receives  nitrogen  and  phosphoric 
acid. 

The  fourth  plot  receives  nitrogen  and  potash. 

The  fifth  plot  receives  nitrogen. 

The  sixth  plot  receives  phosphoric  acid  and  potash. 

The  seventh  plot  receives  potash. 

The  eighth  plot  receives  phosphoric  acid. 


FIELD    TESTS    WITH    FERTILIZERS 


219 


No  fertilizer. 
I. 

N 

K,0 
2. 

N 
P.O5 

3- 

N 
K,0 

4- 

N 
5. 

P.O., 
K,0 

6. 

K,0 

7- 

P.O5 
8. 

Should  good  results  be  obtained  on  plot  No.  3,  the 
indications  are  that  there  is  a  deficiency  of  the  two 
elements  nitrogen  and  phosphoric  acid.  An  increased 
yield  from  No.  4  indicates  deficiency  of  nitrogen  and 
potash.  Under  such  conditions  the  use  of  a  complete 
fertilizer  would  be  unnecessary.  If  No.  5  gives  an 
additional  yield  the  soil  is  in  want  of  nitrogen.  From 
the  eight  plots  it  will  be  possible  to  tell  which  of  the 
various  elements  it  will  be  advisable  to  use.  The  fer- 
tilizers should  be  applied  after  the  land  has  been  thor- 
oughly prepared  and  before  seeding.  Corn  is  a  good 
crop  for  the  first  trials.  The  number  of  plots  may  be 
increased  by  using  well-prepared  stable  manure  and 
gypsum  on  plots  9  and  10  respectively.  The  second 
year  the  results  should  be  verified. 

280.  Deficiency  of  Nitrogen.  —  If  the  results  indi- 
cate a  deficiency  of  nitrogen,  select  two  crops,  one  as 
wheat  which  is  particularly  benefited  by  dressings  of 
nitrogen,  and  another  as  corn  which  has  no  difficulty  in 
obtaining  this  element.  The  cultivation  of  each  crop 
should  be  that  which  experience  has  shown  to  be  the 


220  SOILS    AND    FERTILIZERS 

best.  On  one  wheat,  and  one  corn  plot,  8  pounds  of 
nitrate  of  soda  should  be  used,  a  plot  each  of  wheat 
and  corn  being  left  unfertilized.  If  both  the  corn  and 
the  wheat  are  benefited  by  the  application  of  nitro- 
gen, the  soil  is  in  need  of  available  nitrogen.  If,  how- 
ever, the  wheat  responds  and  the  corn  does  not,  the 
soil  is  not  in  great  need  of  nitrogen  but  does  not  con- 
tain an  abundance  in  available  forms. 

281.  Deficiency  of  Phosphoric  Acid.  —  In  experi- 
menting with  phosphoric  acid,  turnips  are  grown  on 
two  plots  and  barley  on  two  plots.  To  one  plot  of 
each  16  pounds  of  acid  phosphate  are  applied.  If  both 
crops  show  marked  additional  yields  the  soil  is  in  need 
of  available  phosphoric  acid.  If  only  the  turnips  re- 
spond while  the  barley  is  indifferent  the  soil  contains 
a  fair  amount  of  available  phosphoric  acid.  Barley 
and  turnips  are  used  because  there  is  such  a  marked 
difference  in  the  power  of  each  to  assimilate  phos- 
phoric acid. 

282.  Deficiency  of  Potash.  —  In  order  to  determine 
the  condition  of  the  soil  as  to  potash,  potatoes  and  oats 
may  be  used  as  the  trial  crops,  and  8  pounds  of  sul- 
phate of  potash  should  be  applied  to  one  plot  of  each. 
Marked  additional  yields  indicate  a  poverty  of  availa- 
ble potash  ;  an  increased  potato  crop  and  an  indiflfer- 
ent  oat  crop  indicate  potash  not  in  the  most  available 
forms.  If  no  additional  yields  are  obtained  the  soil 
is  not  in  need  of  potash. 


FIELD    TESTS   WITH    FERTILIZERS  221 

283.  Deficiency  of  Two  Elements.  —  If  the  prelim- 
inary trials  indicate  a  deficiency  of  two  elements  as 
nitrogen  and  phosphoric  acid,  both  elements  are  used 
together,  in  the  same  way  as  described  for  deficiency 
of  nitrogen,  with  additional  plots  for  the  separate  ap- 
plication of  nitrogen  and  phosphoric  acid. 

284.  Importance  of  Field  Trials.  —  While  it  seems  a 
troublesome  matter  to  determine  the  actual  needs  of  a 
soil,  it  will  be  found  that  both  time  and  money  are 
saved  by  a  systematic  study  of  the  question.  Suppose 
fertilizers  are  used  in  a  "  hit  or  miss"  way  year  after 
year  on  a  soil,  deficient  only  in  phosphoric  acid.  It 
would  take  8  years  to  find  out  what  the  soil  was 
deficient  in,  if  a  different  fertilizer  were  used  each  year, 
and  during  all  this  period,  either  the  soil  has  failed  to 
receive  its  proper  fertilizer,  or  expensive  and  unneces- 
sary plant  food  has  been  provided. 

285.  Will  it  Pay  to  Use  Commercial  Fertilizers? 

—  This  question  can  be  answered  only  by  trial.  If  a 
soil  is  in  need  of  available  plant  food,  the  additional 
amount  of  crop  produced  should  pay  for  the  fertilizer 
and  the  expense  of  using  it.  Some  fertilizers  have  an 
influence  on  two  or  three  succeeding  crops,  and  only 
partial  returns  are  received  the  first  year.  When  large 
crops  must  be  produced  on  small  areas,  as  in  truck 
farming,  commercial  fertilizers  are  generally  neces- 
sary. In  the  production  of  large  areas  of  staple  crops 
as  wheat    and    corn,    in    the    western   prairie    states, 


222  SOILS   AND    FERTILIZERS 

they  have  never  been  used.  If  the  soil  is  properly 
tilled  and  there  is  a  good  stock  of  natural  fertility,  the 
use  of  commercial  fertilizers  can  be  avoided.  With 
poor  cultivation  and  a  soil  that  has  been  impoverished 
by  injudicious  cultivation  their  use  is  more  necessary. 

286.  Amount  of  Fertilizer  to  Use  per  Acre.  —  When 
commercial  fertilizers  are  used,  it  should  be  the  aim  to 
apply  just  enough  to  produce  normal  yields.  Heavy 
applications  at  long  intervals  are  not  as  productive  of 
good  results  as  light  applications  more  frequently. 
From  400  to  600  pounds  per  acre  is  as  much  as  should 
be  used  at  one  time  unless  previous  trials  have  shown 
that  heavier  applications  are  necessary.  The  way  in 
which  the  fertilizer  is  to  be  applied,  as  broadcast  or 
otherwise,  must  be  determined  by  the  crop  to  be 
grown.  The  fertilizer  should  not  come  in  direct  con- 
tact with  seeds,  neither  should  it  be  worked  into  the 
soil  to  such  a  depth  that  it  may  be  lost  by  leaching 
before  it  can  be  appropriated  by  the  crop. 

287.  Excessive  Applications  of  Fertilizers  Injuri- 
ous. —  An  overabundance  of  plant  food  has  an  inju- 
rious effect  upon  crop  growth.  Plants  take  their 
food  from  the  soil  in  dilute  solutions,  and  when 
the  solution  is  concentrated  abnormal  growth  results. 
Potatoes  heavily  manured  with  nitrate  of  soda  make  a 
luxuriant  growth  of  vines  but  produce  only  a  few 
small  tubers.  When  a  medium  dressing  is  used  along 
with  potash    and  phosphoric    acid,  a    more    balanced 


FIELD    TESTS    WITH    FERTILIZERS  223 

growth  is  obtained,  and  a  better  yield  is  the  result. 
Heavy  applications  of  nitrate  of  soda  produce  a  rank 
o^rowth  of  straw,  with  a  low  yield  of  grrain.  The  ex- 
cessive  amount  of  nitrogen  causes  the  mineral  matter 
to  be  utilized  for  straw  production  and  leaves  only  a 
small  amount  for  grain  production.  When  applica- 
tions of  commercial  fertilizers  are  too  heavy,  plants 
take  up  unnecessary  amounts  of  food  and  fail  to  make 
good  use  of  it.  In  fact  crops  may  be  overfed  the 
same  as  animals.  Hence  in  the  use  of  fertilizers  ex- 
cessive applications  are  to  be  avoided. 

288.  Fertilizing  Special  Crops. — There  are  crops 
which  need  special  help  in  obtaining  some  one  ele- 
ment, and  in  the  use  of  fertilizers  it  should  be  the  rule 
to  help  those  crops  which  have  the  greatest  difficulty 
in  obtaining  food.  When  the  soil  does  not  show  a 
marked  deficiency  in  any  one  element,  light  dressings 
of  special  purpose  manures  may  be  made  to  the  follow- 
ing crops  : 

Wheat.  —  Nitrogen  first  ;  phosphoric  acid  to  a  less 
extent. 

Barley^  oats^  and  rye  require  manuring  like  wheat, 
but  to  a  less  extent.  Each  crop  has  a  different  power 
of  obtaining  nitrogen.  Wheat  requires  the  most  help 
and  barley  and  rye  the  least. 

Corn.  —  Phosphoric  acid  first  ;  then  nitrogen  and 
potash. 


224  SOILS   AND    FERTILIZERS 

Potatoes.  — General  manuring  ;  reenforced  with  pot- 
ash. 

Ma  ngels.  -^  N  i  tr ogen . 
Turiiips.  —  Phosphoric  acid. 
Clover.  —  Lime  and  potash. 
Timothy. — General  manuring. 

289.  Commercial  Fertilizers  and  Farm  Manures. 

— '  Commercial  fertilizers  should  not  replace  farm  ma- 
nures, but  simply  reenforce  them.  Although  com- 
mercial fertilizers  are  called  complete  manures,  they 
fail  to  supply  organic  matter.  It  is  more  important  in 
some  soils  than  in  others,  that  the  organic  matter  be 
maintained  because  in  some  soils  the  organic  matter 
takes  a  more  important  part  in  crop  production  than 
does  the  food  applied  in  commercial  forms.  For 
example,  when  a  rich  prairie  soil  is  reduced  by  grain 
cropping  and  is  allowed  to  return  to  pasture,  heavier 
yields  of  grain  are  afterwards  obtained  than  from  sim- 
ilar soils  which  received  applications  of  commercial 
fertilizers. 


CHAPTER  XI 

FOOD  REQUIREMENTS  OF  CROPS 

290.  Amount  of  Fertility  Removed  by  Crops.  — 

From  an  acre  of  soil,  producing  average  crops,  the 
amount  of  fertility  removed  varies  between  wide  lim- 
its. For  example,  an  acre  of  mangels  removes  150 
pounds  of  potash,  while  an  acre  of  flax  removes  27 
pounds ;  an  acre  of  corn  removes  about  75  pounds  of 
nitrogen,  while  an  acre  of  wheat  removes  about  35 
pounds.  Crops  w^hich  remove  the  most  fertility  do 
not  always  require  the  most  help  in  obtaining  their  food. 
This  is  because  the  amount  of  plant  food  assimilated, 
and  the  power  of  crops  to  obtain  this  food,  are  not 
the  same.  An  acre  of  corn,  for  example,  takes  over 
twice  as  much  nitrogen  as  an  acre  of  wheat,  but  wheat 
will  often  leave  the  soil  in  a  more  impoverished  con- 
dition than  corn,  because  corn  has  greater  power  for 
procuring  nitrogen  and  for  utilizing  that  formed  by 
nitrification  after  the  wheat  crop  has  completed  its 
growth.  The  available  nitrogen  if  not  utilized  by  a 
crop  may  be  lost  in  various  ways.  IVIangels  require 
about  twice  as  much  phosphoric  acid  as  flax,  but  are 
a  strong  feeding  crop  and  require  less  help  in  obtain- 
ing this  element. 

It  was  formerly  believed  that  the  amoimt  of  plant 


226  SOILS   AND    FERTILIZERS 

food  present  in  the  matured  crop  indicated  the  kind 
and  amount  of  fertilizing  ingredients  to  apply,  and 
that  a  correct  system  of  manuring  required  a  return 
to  the  soil  of  all  elements  removed  in  the  crop.  Ex- 
periments have  shown  that  both  of  these  views  are  in- 
correct. The  composition  of  plants  cannot  be  taken  as 
the  basis  for  their  manuring.  For  example  an  acre  of 
wheat  contains  35  pounds  of  nitrogen  while  an  acre  of 
clover  contains  70  pounds.  If  70  pounds  of  nitrogen 
were  applied  to  an  acre  of  clover  and  35  pounds  to  an 
acre  of  wheat,  poor  results  would  follow,  because  clo- 
ver can  obtain  its  own  nitrogen  while  wheat  is  nearly 
helpless  in  obtaining  it,  and  the  35  pounds  would  not 
necessarily  come  in  contact  with  the  roots  so  that  it 
could  all  be  assimilated.  While  the  amount  of  plant 
food  removed  in  crops  cannot  serve  as  the  basis  for  their 
manuring,  valuable  results  are  obtained  from  the  study 
of  the  different  elements  of  fertility  removed  in  crops, 
and  in  making  use  of  the  following  figures,  other  fac- 
tors, as  the  influence  of  the  crop  upon  the  soil  and  the 
power  of  the  crop  to  obtain  its  food,  must  also  be  con- 
sidered. 


FOOD    REQUIREMENTS   OF    CROPS  227 

Pi^ANT  Food  Removed  by  Crops''^ 

Pounds  per  acre. 
Phos- 
Gross       Nitro-     phoric      Pot-  Sil-      Total 

Crops.  weight.      gen.         acid.        ash.  Lime.     ica.       ash. 

Wheat,  20  bus 1200         25         12.5         7         i         i         25 

straw 2000         10  7.5       28         7     115       185 

Total 35         20  35         8     116       210 

Barley,  40  bus 1920         28         15  81       12         40 

Straw 3000         12  5  30         8       60       176 

Total 40         20  38         9       72       216 

-   Oats,  50  bus 1600        35         12  10         1.5    15         55 

Straw 3000         15  6  35'        9.5 '  60       150 

Total 50         18  45       II. o   75       205 

Corn,  65  bus 2200  40  18  15  i  i  40 

Stalks 3000  35  2  45  II'  89  160 

Total 75  20  60  12  90  200 

Peas,  30  bus 1800  ..  18  22  4  i  64 

Straw 3500  ..  7  38  71  9  176 

Total . .  25  60  75  10  240 

Mangels,  10  tons..   20000         75         35         150       30       10       350 

Meadow  hay,  i  ton     2000        30         20  45       12       50       175 

Red    Clover  Hay, 

2  tons 4000         ..         28  66       75       15       250 

Potatoes,  150  bus..     9000  40  20  75       25  4  125 

Flax,  15  bus 900  39  15  83  0.5  34 

Straw 1800  15  3  19       13  3  53 

Total 54  18  27       16  3-5  87 

291.  Plants  Render  Their  Own  Food  Soluble.  —  It 

was  supposed  at  one  time  that  plants  obtained  all  of 
their  mineral  food  from  the  mineral  matter  dissolved 
in  the  soil  water.  Experiments  by  Liebig  demonstra- 
ted that  plants  have  the  power  of  rendering  their  own 
food   soluble,    provided    it   does   not   exist    in  forms 


228  SOILS   AND    FERTILIZERS 

too  inert  to  undergo  chemical  change.  Liebig  grew 
barley  in  boxes  so  constructed  that  all  of  the  water- 
soluble  plant  food  could  be  secured.  Two  of  the  boxes 
were  manured  and  two  left  unmanured.  In  one  box 
which  received  manure  and  one  which  received  none, 
barley  was  grown.  One  each  of  the  manured  and 
unmanured  boxes  was  left  barren.  He  collected  all  of 
the  drain  waters  and  determined  the  soluble  mineral 
matter  present,  also  weighed  and  analyzed  the  crop. 
His  results  showed  that  92  per  cent,  of  the  potash  in 
the  crop  was  obtained  from  forms  insoluble  in  water. ^^ 

In  the  roots  of  all  plants  there  are  present  various 
organic  acids.  Between  the  rootlet  and  the  soil  there 
is  a  layer  of  water.  The  plant  sap  and  the  soil  water 
are  separated  by  plant  tissue  which  acts  as  a  membrane. 
All  of  the  conditions  are  favorable  for  osmosis.  The 
acid  sap  from  the  roots  finds  its  way  into  the  soil  in 
exchange  for  some  of  the  soil  water.  This  acid,  excre- 
ted by  the  roots,  acts  upon  the  mineral  matter,  render- 
ing it  soluble,  when  it  is  taken  up  by  the  plant. 
Different  plants  contain  different  kinds  and  amounts 
of  organic  acids  as  well  as  present  different  areas  of 
root  surface  to  act  upon  the  soil,  and  the  result  is  that 
agricultural  crops  have  different  powers  of  assimila- 
ting food. 

Plants  not  only  possess  the  power  of  rendering  their 
food  soluble  but  they  are  also  able  to  select  their  own 
food  and  to  reject  that  which  is  unnecessary.     For  ex- 


CEREAL   CROPS  229 

ample,  wheat  grrown  on  prairie  soil  containing  soda  in 
equally  abundant  and  soluble  forms  as  the  potash,  will 
contain  relatively  little  soda  compared  with  the  potash 
in  the  crop.^^ 

CEREAL  CROPS 

292.  General  Food  Requirements.  —  Cereal  crops  con- 
tain a  high  per  cent,  of  silica  and  evidently  possess 
the  power  of  feeding  upon  some  of  the  simpler  silicates 
of  the  soil, 73  liberating  the  base  elements  which  are 
utilized  as  food,  while  the  silica  is  deposited  in  the 
outer  surface  of  the  straw.  As  previously  stated,  cer- 
eal crops  although  they  do  not  remove  large  amounts 
of  total  nitrogen  from  the  soil  require  special  help  in 
obtaining  this  element.  There  is,  however,  a  great 
difference  among  the  cereals  as  to  power  of  assimila- 
ting nitrogen.  Next  to  nitrogen  these  crops  stand 
most  in  need  of  phosphoric  acid.  The  humic  phos- 
phates are  utilized  by  nearly  all  of  the  cereals. 

293.  Wheat.  —  This  crop  is  more  exacting  in  its 
food  requirements  than  barley,  oats,  or  rye.  Wheat 
is  comparatively  a  weak  feeding  crop,  and  the 
soil  should  be  in  a  higher  state  of  fertility  than  for 
other  grains.  The  extensive  experiments  of  Lawes 
and  Gilbert  have  given  valuable  information  regard- 
ing the  effects  of  manures  on  wheat.  The  results  are 
given  in  the  following  table  -J"^ 


230  SOILS   AND    FERTILIZERS 

Average  Yiei^d  of  Wheat  per  Acre. 

Bushels. 

No  manure  for  40  years 14 

Minerals  alone  for  32    years  15^ 

Nitrogen     "        "     "      "       23^ 

Farmyard  manure  for  32  years 32| 

Minerals  and  nitrogen  for  32  years' 36^^ 

0-^4 

The  food  requirements  of  wheat  are  such  that  it  should 
be  given  a  favored  position  in  the  rotation.  Wheat  may 
follow  clover  provided  the  clover  sod  is  light  and  is 
fall  plowed.  On  some  soils,  however,  wheat  does  not 
thrive  following  a  sod  crop.  It  takes  nearly  a  year 
for  a  heavy  sod  residue  to  get  into  suitable  food  forms 
for  a  wheat  crop.  Under  such  conditions,  oats  should 
first  be  sown,  then  wheat  may  follow.  On  average 
soil  a  medium  clover  sod,  plowed  late  in  summer  or  in 
early  fall,  and  followed  with  surface  cultivation,  leaves 
the  land  in  good  condition  for  spring  wheat.  It  is  not 
advisable  to  have  wheat  follow  barley,  because  the 
soil  will  be  too  porous,  and  barley  being  a  stronger 
feeding  crop  leaves  the  land  in  poor  condition  as  to 
available  plant  food.  When  a  corn  crop  is  well  ma- 
nured, wheat  may  follow.  The  food  requirements  of 
wheat  are  best  satisfied  following  a  light,  w^ell  cultiva- 
ted clover  sod,  or  following  oats  which  have  been  grown 
on  heavy  sod,  or  following  corn  that  has  been  well 
manured. 

1  86  pounds  of  nitrogen  as  sodium  nitrate. 

2  86        "         *'  "  "     ammonium  salts. 


CEREAL   CROPS  23 I 

294.  Barley.  —  While  wheat  and  barley  belong  to 
the  same  general  class  of  cereals,  they  differ  greatly  in 
their  habits  and  food  requirements.  Barley  is  a 
stronger  feeding  crop,  has  a  greater  root  development 
near  the  surface,  and  can  utilize  food  in  cruder  forms. 
In  many  of  the  western  states,  soils  which  produce 
poor  wheat  crops,  from  too  long  cultivation,  give  ex- 
cellent yields  of  barley.  This  is  due  to  changed  con- 
ditions, of  both  the  chemical  and  mechanical  composi- 
tion of  the  soil.  Long  cultivation  has  made  the  soil 
porous  and  reduced  the  nitrogen  content.  Barley 
thrives  best  on  a  rather  open  soil  and  has  greater  ni- 
trogen assimilative  powers  than  wheat.  Barley,  how- 
ever, responds  liberally  to  manuring,  particularly  to  ni- 
trogenous manures.  The  experiments  of  Lawes  and 
Gilbert  on  the  growth  of  barley  are  briefly  summa- 
rized in  the  following  tablets 

Average  Yield  of  Barley  Per  Acre  for  34  Years. 

Bushels. 

No  manure 17I 

Superphosphate  alone 23I 

Mixed  minerals 2\\ 

Nitrogen  alone 3o| 

Nitrogen  and  superphosphate 45 

Farmyard  manures 49I 

295.  Oats.  —  Oats  are  capable  of  obtaining  food  un- 
der more  adverse  conditions  than  either  barley  or 
wheat.  They  are  also  less  exacting  as  to  soil  require- 
ments.    The  oat  plant  will  adapt  itself  to  either  sandy 


232  SOILS   AND    FERTILIZERS 

or  clay  soil,  and  will  thrive  in  the  presence  of  alkaline 
matter  or  humic  acid  where  wheat  would  be  destroyed. 
In  a  rotation,  oats  usually  occupy  a  position  less  favored 
by  manures.  They  are,  however,  greatly  benefited  by 
fertilizers  particularly  by  those  of  a  nitrogenous  na- 
ture. 

296.  Corn.  —  Experiments  with  corn  indicate  that 
under  ordinary  conditions  it  requires  most  help  in  ob- 
taining phosphoric  acid.  Corn  removes  a  large  amount 
of  gross  fertility  but  its  habits  of  growth  are  such  that 
it  generally  leaves  an  average  soil  in  better  condition 
for  succeeding  crops.  Corn  is  not  injured  as  are  many 
grain  crops  by  heavy  applications  of  stable  manure. 
It  does  not,  like  flax,  produce  waste  products  which 
are  destructive  to  itself.  Rich  prairie  soils  when 
newly  broken  give  better  results  for  wheat  culture 
after  one  or  two  corn  crops  have  been  removed.  The 
food  requirements  of  corn  are  satisfied  by  applications 
of  stable  manure,  occasionally  reenforced  with  a  little 
phosphoric  acid.  After  clover,  corn  gives  excellent 
returns,  and  when  corn  is  the  chief  market  crop  it 
should  be  favored  by  having  the  best  position  in  a  ro- 
tation. 

MISCELLANEOUS   CROPS 

297.  Flax    is  very    exacting  in   food    requirements 
and  for  its  culture  the  soil  must  be  in  a  high  state  of. 
fertility.     It  is  a  type  of  a  weak  feeding  crop.     There 
are  but  few  roots  near  the  surface  and  consequently  it 


MISCELLANEOUS    CROPS  233 

has  restricted  powers  of  nitrogen  assimilation. 37  Flax 
does  not  remove  a  large  amount  of  fertility  but  if 
grown  too  frequently  the  tendency  is  to  get  the  land 
out  of  condition  rather  than  to  exhaust  it.  Flax 
should  be  indirectly  manured.  Direct  applications  of 
stable  manure  produce  poor  results,  but  when  the  ma- 
nure is  applied  to  the  preceding  crop  excellent  results 
are  obtained.  The  best  conditions  for  flax  culture  re- 
quire that  it  should  be  grown  on  the  same  land  only 
once  in  five  years.  Dr.  Lugger  has  demonstrated 
that  there  are  produced,  when  the  roots  and  straw  of 
ilax  decay,  products  which  are  destructive  to  succeed- 
ing flax  crops. 7^  The  food  requirements  of  flax  are 
met  when  it  follows  corn  which  has  been  well  manured, 
or  a  sod  which  has  been  given  the  cultivation  described 
for  wheat.  Flax  and  spring  wheat  are  much  alike  in 
food  requirements. 

298.  Potatoes.  —  Potatoes  are  surface  feeders  and 
when  grown  continually  upon  the  same  soil  without 
manure,  the  yield  per  acre  decreases  more  rapidly  than 
any  other  farm  crop.  Experiments  with  potatoes  by 
Lawes  and  Gilbert  using  different  manures  gave  the 
following  result  r^^ 

Average  Yield  per  Acre  for  12  Years. 

Tons.  Cwt. 

No  manure i  19I 

Superphosphate 3  5 

Minerals  alone 3  7| 

Nitrate  of  soda  alone 2  4| 

Mixed  manures  and  nitrogen 5  lyf 

Farm  manures,  alternate  years 4  3| 


234  SOILS   AND    FERTILIZERS 

Potatoes  require  liberal  general  manuring  reenforced 
with  wood  ashes  or  other  potash  fertilizers.  In  the 
rotation  they  should  follow  grain  or  pasture  land,  pro- 
vided the  fertility  of  the  soil  is  kept  up. 

299.  Sugar-beets.  —  This  crop  is  more  exacting  in 
its  food  demands  than  other  root  crop.  Excessive 
fertility  is  not  conducive  to  a  high  content  of  sugar. 
Soils  in  a  medium  state  of  fertility  usually  give  the 
best  results. 7^  Sugar-beets  should  not  receive  heavy 
dressings  of  stable  manure,  because  an  abnormal 
grow^th  results.  Nitrogenous  fertilizers  can  be  ap- 
plied only  in  limited  amounts,  heavier  dressings  of 
potash  and  phosphoric  acid  are  more  admissible. 
When  sugar-beets  follow^  corn  which  has  been  manured, 
or  grain  which  has  left  the  soil  in  an  average  state  of 
fertility,  the  food  requirements  are  well  met. 

300.  Roots.  —  Mangels  are  gross  feeders  and  re- 
move a  larger  amount  of  fertility  from  the  soil  than 
any  other  farm  crop."  When  fed  to  stock  and  the 
manure  is  returned  to  the  soil  they  materially  aid  in 
making  the  plant  food  more  available  for  delicate 
feeding  crops.  Mangels  are  better  able  to  obtain  their 
phosphoric  acid  than  are  turnips  and  need  the  most 
help  in  the  way  of  nitrogen.  Turnips  are  surface 
feeders  with  stronger  power  of  nitrogen  assimilation 
than  the  grains  but  with  restricted  power  of  phosphate 
assimilation.  Manures  for  turnips  should  be  phos- 
phatic  in  nature. 


MISCELLANEOUS    CROPS  235 

301.  Rape  is  a  type  of  a  strong  feeding  plant  capa- 
ble of  obtaining  its  food  under  conditions  adverse  to 
grain  culture.  When  grown  too  frequently  upon  the 
same  soil  it  does  not  thrive.  On  account  of  its  great 
capacity  for  obtaining  food,  it  is  a  valuable  crop  to 
use  for  green  manuring  purposes.  ^9 

302.  Buckwheat  is  a  strong  feeding  crop  and  its 
demands  for  food  are  easily  met.  On  rich  soil,  a  rank 
growth  of  straw  results,  with  poor  seed  formation. 
Buckwheat  is  usually  sown  upon  the  poorest  soil  of 
the  farm.  Being  a  strong  feeder  it  is  frequently  used 
as  a  manurial  crop,  being  plowed  under  while  green  to 
serve  as  food  for  weaker  feeding  crops. 

303.  Cotton. — On  average  soils  cotton  stands  in 
need  first  of  phosphoric  acid,  second  of  nitrogen.^  It 
is  most  able  to  obtain  potash,  but  soils  deficient  in  pot- 
ash require  its  use.  Organic  nitrogen  as  cottonseed 
meal  and  stable  manure  appear  equally  as  effective  as 
nitric  nitrogen.  Phosphoric  acid  must  be  applied  in 
the  most  available  forms.  In  fertilizing  cotton, 
the  use  of  green  manuring  crops  as  cow  peas  with  an 
application  of  marl  gives  beneficial  results.  Marl,  how- 
ever, should  not  be  applied  alone  because  of  the  forma- 
tion of  insoluble  phosphate  of  lime.  Lime  combines 
with  the  decaying  organic  matter  in  preference  to 
phosphates,  a  result  which  is  beneficial  to  both  soil 
and  crop. 

304.  Hops.  —  The  hop  plant  is  peculiar  in  regard 


236  SOILS   AND    FERTILIZERS 

to  its  food  requirements.  An  excess  of  easily  soluble 
plant  food  is  injurious  while  a  lack  is  equally  so.  An 
abundance  of  food  in  organic  forms  is  most  essential. 
Heavy  dressings  of  farm  manures  may  be  applied. 
Where  hops  are  grown  there  is  a  tendency  to  use  all 
of  the  manure  on  the  hops  while  the  rest  of  the  farm 
is  left  unmanured.  Very  light  applications  of  com- 
mercial fertilizers  may  be  used  in  connection  with  sta- 
ble manure,  but  such  use  should  be  made  only  after  a 
preliminary   trial  on  a  smaller  scale. 

305.  Hay  and  Grass  Crops.  —  Most  grass  crops  have 
shorter  roots  than  grain  crops  ;  they  are  surface  feed- 
ers and  not  so  able  to  secure  mineral  food.  When  a 
number  of  crops  have  been  removed  the  soil  may  stand 
in  need  of  available  mineral  matter.  Farm  manures 
are  particularly  well  adapted  for  fertilizing  grass.  Ap- 
plications of  nitrogenous  manures  result  in  discoura- 
ging the  growth  of  clover.  Heavy  manuring  of  grass 
land  has  a  tendency  to  reduce  the  number  of  species 
and  one  kind  is  apt  to  predominate.^'  On  some  soils 
ashes,  and  on  others  lime  fertilizers,  have  been  found 
very  beneficial.  The  manuring  of  grass  lands  must 
be  varied  to  meet  the  requirements  of  different  soils. 
Permanent  meadows  require  different  manuring  from 
meadow  simply  introduced  as  an  important  crop  in  the 
rotation. 

306.  Leguminous  Crops.  —  For  leguminous  crops  pot- 
ash and  lime  fertilizers  have  been  found  of  most  value. 


MISCELLANEOUS    CROPS  237 

Analyses  of  leguminous  crops,  as  clover  and  peas,  show 
large  amounts  of  both  potash  and  lime.  Many  crops 
as  clover  fail  when  grown  too  frequently  upon  the 
same  soil,  not  because  the  soil  is  exhausted  but  because 
of  the  development  in  the  soil  of  organic  products 
which  are  destructive  to  growth.  When  the  inexpen- 
sive food  requirements  of  leguminous  crops  are  sup- 
plied, the  soil  is  enriched  with  nitrogen  and  phos- 
phoric acid  which  have  been  changed  to  more  availa- 
ble forms. 


CHAPTER  XII 

ROTATION  OF  CROPS  AND  CONSERVATION  OF  SOIL 
FERTILITY 

307.  Object  of  Crop  Rotation.  —  The  object  of  the 
systematic  rotation  of  crops  is  to  conserve  the  fertility 
of  the  soil,  and  at  the  same  time  to  produce  larger 
yields.  In  order  to  accomplish  this,  the  food  require- 
ments of  different  crops  must  be  met  by  good  cultiva- 
tion and  proper  manuring.  Rotations  must  be  planned 
according  to  the  nature  of  the  soil  and  the  system  of 
farming  that  is  to  be  followed.  For  general  grain 
farming  a  different  system  must  be  practiced  than  for 
exclusive  dairying.  Whatever  the  nature  of  farming 
the  whole  farm  should  gradually  undergo  a  systematic 
rotation.  If  the  farm  is  uneven  in  soil  texture,  differ- 
ent rotations  must  be  practiced  on  the  various  parts. 
There  is  no  w^ay  in  which  soils  are  more  rapidly  de- 
pleted of  fertility  than  by  the  continued  culture  of  one 
crop.  In  exclusive  wheat  raising  for  example  the 
losses  w^hich  occur  are  not  confined  to  the  fertilit}'  re- 
moved in  the  crop  but  may  take  place  in  other  ways 
as  described  in  the  chapter  on  nitrogen.  When  wheat 
is  properly  grown  in  alternation  with  other  crops, 
losses  of  nitrogen  are  reduced  to  the  minimum. 

When  remunerative  crops  can  no  longer  be  produced 
the  soil  is  said  to  be  exhausted.     Soil  exhaustion  may 


ROTATION    OF    CROPS  239 

be  due  either  to  a  lack  of  fertility  or  to  getting  the 
soil  out  of  condition  because  of  the  "one-crop  system" 
and  poor  methods  of  cultivation. 

308.  Principles  Involved  in  Crop  Rotation. — In 
the  systematic  rotation  of  crops  there  are  a  few  funda- 
mental principles  with  which  all  rotations  should  be 
made  to  conform.     Briefly  stated  these  principles  are  : 

1.  Deep  and  shallow  rooted  crops  should   alternate. 

2.  Humus-consuming  and  humus-producing  crops 
should  alternate. 

3.  Crops  should  be  rotated  so  as  to  make  the  best 
use  of  the  preceding  crop  residue. 

4.  Crops  should  be  rotated  so  as  to  secure  nitrogen 
indirectly  from  atmospheric  sources. 

5.  Crops  should  be  rotated  so  as  to  keep  the  soil  in 
the  best  mechanical  condition. 

6.  In  arid  regions  crops  should  be  rotated  so  as  to 
make  the  best  use  of  the  soil  water. 

7.  An  even  distribution  of  farm  labor  should  be  se- 
cured by  a  rotation. 

8.  Farm  manures  and  fertilizers  should  be  used  in 
the  rotation  where  they  will  do  the  most  good. 

9.  Rotations  should  be  planned  so  as  to  produce  fod- 
der for  stock,  and  so  that  every  vear  there  will  be  some 
important  crop  to  be  sold. 

309.  Deep  and  Shallow  Rooted  Crops.  —  When 
deep  and  shallow  rooted  crops  alternate,  the  draft  upon 
the  surface  soil  and  subsoil  is  more  evenly  distributed. 


240  SOILS    AND    FERTILIZERS 

In  many  soils  nitrogen  and  phosphoric  acid  are  more 
abnndant  in  the  surface  soil  while  potash  and  lime 
predominate  in  the  subsoil.  When  such  a  condition 
exists,  the  alternating  of  deep  and  shallow  rooted 
crops  is  very  beneficial,  because  the  surface  soil  is  re- 
lieved of  continuous  heavy  drafts  upon  the  elements 
present  in  scant  amounts. 

310.  Humus-consuming  and  Humus-producing 
Crops.  —  When  grain  or  hoed  crops  are  grown  con- 
tinuously, oxidation  of  the  humus  occurs,  and  the 
chemical  and  physical  properties  of  the  soil  may  be 
entirely  changed  by  the  loss  of  the  humus.  The  ro- 
tating of  grass  and  grain  crops  and  the  use  of  stable 
manure  serve  to  maintain  the  humus  equilibrium.  On 
some  soils  lime  may  be  required  along  with  the  humus 
to  prevent  the  formation  of  humic  acid,  and  in  such 
cases  the  best  conditions  exist  when  both  lime  and  hu- 
mus materials  are  supplied.  The  alternation  of  hu- 
mus-producing and  humus-consuming  crops  is  one  of 
the  essential  matters  to  consider  in  a  rotation. 

311.  Crop  Residue.  —  Crop  residues  should  always 
be  placed  at  the  disposal  of  weak  feeding  crops.  For 
example,  after  a  light  clover  and  timothy  sod,  wheat 
or  flax  should  be  grown  in  preference  to  barley  or 
mangels.  The  weak  feeding  crop  should  then  be  fol- 
lowed by  a  strong  feeding  crop,  and  each  is  properly 
supplied  with  food.  It  would  be  poor  economy,  on  an 
average  soil,  to  follow  clover  and  timothy  with  mangels, 


ROTATION    OF    CROPS  24 1 

then  with  barley,  and  finally  with  flax,  because  the 
flax  would  be  placed  at  a  serious  disadvantage  follow- 
ing two  strong  feeding  crops.  If  reversed,  the  crops 
would  be  placed  in  order  of  assimilative  pow^r,  and  the 
best  use  w^ould  be  made  of  the  sod  crop  residue. 
When  crops  of  dissimilar  feeding  habits  follow  each 
other  in  rotation  not  only  are  the  crop  residues  used  to 
the  best  advantage,  but  the  soil  is  relieved  of  excessive 
demands  on  special  elements.  For  example,  wheat 
and  clover  take  different  amounts  of  potash  and  lime 
from  the  soil.  Wheat  has  the  power  of  feeding  upon 
silicates  of  potash  which  clover  cannot  assimilate, 
hence  wheat  and  clover  in  rotation  relieve  the  soil  of 
excessive  demands  on  the  potash. 

312.  Nitrogen-consuming  and  Nitrogen-producing 
Crops.  —  It  is  possible  in  a  five-course  rotation  to  main- 
tain or  even  increase  the  nitrogen  of  the  soil  without 
the  use  of  nitrogenous  manures.  In  Section  131  an  ex- 
ample is  given  of  a  rotation  which  has  left  the 
soil  with  a  better  supply  of  nitrogen  than  at  the  begin- 
ning. W^hen  a  soil  produces  a  good  clover  crop  once 
in  five  years,  and  stable  manure  is  used  once  during 
the  rotation,  the  soil  nitrogen  is  not  decreased.  By 
means  of  rotating  nitrogen-producing  and  nitrogen- 
consuming  crops  it  is  possible  to  sell  nitrogenous  grain 
products  from  the  farm  without  purchasing  nitroge- 
nous manures.  The  conservation  of  the  nitrogen  of 
the  soil  is  the  most  important  point  to  consider  in  the 


242  SOILS    AND    FERTILIZERS 

rotation  of  crops,  because  it  is  the  most  expensive  ele- 
ment and  is  the  most  liable  to  be  deficient. 

313.  Influence  of  Rotation  upon  the  Mechanical 
Condition  of  Soils.  —  With  different  kinds  of  crops, 
the  mechanical  conditions  of  soils  are  constantly  under- 
going change.  Grain  crops  and  hoed  crops  tend  to 
make  the  soil  open  in  texture.  Grass  crops  have  the 
opposite  effect.  All  soils  should  undergo  periodic 
compacting  and  loosening.  Some  require  more  of  one 
treatment  than  of  the  other.  In  a  good  rotation  the 
mechanical  action  of  the  crop  upon  the  soil  should  be 
considered,  otherwise  the  soil  may  get  into  poor  condi- 
tion to  retain  water  or  become  so  loose  that  heavy 
losses  occur  through  wind  storms.  Sandy  soils  are 
improved  by  those  methods  of  cropping  which  compact 
the  soil,  while  heavy  clays  require  the  opposite  treat- 
ment. The  rotation  should  be  made  to  conform  to 
the  requirements  of  the  soil. 

314.  Economic  Use  of  Soil  Water.  —  The  rotation 
should  not  be  of  such  a  nature  as  to  make  excessive 
demands  upon  the  soil  water.  For  example,  after  a 
grain  crop  has  been  produced,  it  is  best  in  regions  of 
scant  rainfall  to  plow  the  land  and  get  it  into  condi- 
tion to  conserve  the  water  for  the  next  year's  crop, 
rather  than  to  attempt  to  raise  a  catch  crop  the  same 
year.  Crops  removing  excessive  amounts  of  water 
should  not  be  grown  too  frequently.  Sunflowers,  for 
example,  remove  twenty  times  more  water  than  grain 


ROTATION    OF    CROPS  243 

crops.  Cabbage  removes  from  the  soil  more  water 
than  many  other  crops.  With  a  good  rotation  it  is 
possible  to  carr\'  the  water  balance  in  the  soil  from 
year  to  year,  so  that  crops  will  be  supplied  in  times  of 
drought. 

315.  Rotation  and  Farm  Labor.  —  The  rotation  of 
crops  should  be  planned  so  that  an  even  distribution 
of  farm  labor  is  secured.  The  importance  of  this 
principle  is  so  plain  that  its  discussion  is  unnecessary. 
It  is  a  topic  outside  of  the  domain  of  chemistry, 
but  is  nevertheless  one  of  the  most  important  to  con- 
sider in  economic  farming,  and  should  not  be  lost 
sight  of  in  planning  rotations. 

316.  Economic  Use  of  Manures.  —  Farm  manure 
should  be  applied  to  those  crops  which  experience  has 
shown  to  be  the  most  benefited  bv  its  use.  At  least 
once  during  a  five  years'  rotation  the  land  should  receive 
a  dressing  of  stable  manure.  If  commercial  fertilizers 
are  used,  they  should  be  applied  to  the  crops  which 
require  the  most  help  in  obtaining  food.  With  the 
growing  of  clover  and  the  use  of  farm  manures,  only 
the  poorer  kinds  of  soil  will  require  commercial  fertil- 
izers for  general  crop  production.  It  is  more  econom- 
ical to  reenforce  the  farm  manures  with  fertilizers 
especially  adapted  to  the  soil  and  crop  than  to  purchase 
complete  fertilizers. 

317.  Salable  Crops. —  In  all  farming,  something 
must  be  sold  from  the  farm.     It  should  be  the  aim  to 


244  SOILS   AND    FERTILIZERS 

sell  products  which  remove  the  least  fertility,  or  if 
those  are  sold  which  remove  large  amounts,  to  return 
in  cheaper  forms  the  fertility  sold.  In  a  good  rotation 
it  is  the  plan  to  have  at  least  one  salable  crop 
each  year.  The  whole  farm  need  not  undergo  the 
same  rotation  at  the  same  time  and  the  rotation  may 
be  subject  to  minor  changes  as  circumstances  require. 
To  illustrate,  wheat  and  flax  occupy  about  the  same 
position  in  a  rotation.  If  when  the  crop  is  to  be 
seeded  the  indications  are  that  wheat  will  be  a  poor 
paying  crop  and  flax  sell  well,  flax  should  be  sown. 
The  rotation  should  be  such  that  one  of  two  or  three 
crops  may  be  grown  as  circumstances  require. 

318.  Rotations  Advantageous  in  Other  Ways.  —  A 
good  rotation  will  be  found  advantageous  in  many 
ways.  With  one  line  of  cropping,  land  becomes  foul 
with  special  kinds  of  weeds  which  are  unable  to 
thrive  when  crops  are  rotated.  Frequently  the  rota- 
tion must  be  planned  so  as  to  reclaim  the  land  from 
'Vv^eeds. 

Relief  from  insect  pests  is  often  secured  by  a  proper 
rotation.  Many  insects  are  capable  of  living  only  on 
a  special  crop  and  when  this  crop  is  grown  continually 
on  the  same  land  the  best  conditions  for  insect  ravages 
exist. 

319.  Long-  and  Short-course  Rotations.  —  Rota- 
tions vary  in  length  from  2  to  1 7  years.      Long-course 


ROTATION    OF    CROPS  245 

rotations  are  more  generally  followed  in  Enropean 
countries.  The  length  of  the  rotation  can  only  be  de- 
termined bv  the  conditions  existing;  in  different  local- 
ities.  As  a  general  rule  long-course  rotations  should 
be  attempted  only  after  a  careful  study  of  all  the 
conditions  relating  to  the  system  of  farming  that  it  is 
desired  to  follow.  For  northern  latitudes  a  rotation 
of  four  or  five  years  ogives  excellent  results.  In  some 
localities  three-course  rotations  are  the  most  desirable. 

A  rotation  that  is  suitable  for  one  locality  or  kind 
of  farming  may  be  unsuited  for  other  localities  or  con- 
ditions. Because  of  variations  in  soil,  climate,  and 
rainfall,  no  definite  standard  rotation  can  be  pro- 
posed that  will  be  suitable  for  all  conditions. 

320.  Example  of  Rotation.  —  In  dealing  with  the 
subject  of  rotations  it  is  best  to  take  actual  problems 
as  they  present  themselves  and  plan  rotations  that  will 
best  meet  all  conditions.  For  example,  a  farm  of 
160  acres  is  to  be  rotated  with  the  main  object  of  pro- 
ducing fodder  for  live  stock,  and  a  small  amount  of 
grain  for  sale.  The  following  rotation  has  been  pro- 
posed to  meet  such  conditions.  ^^ 


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248  SOILS    AND    FERTILIZERS 

The  farm  is  divided  into  eight  fields  of  20  acres 
each ;  seven  fields  are  brought  under  the  rotation, 
while  one  field  is  left  free  for  miscellaneous  purposes. 
Each  year  there  are  produced  20  acres  of  corn,  20 
acres  of  timothy  and  clover  hay,  10  acres  each  of 
wheat  and  flax,  20  acres  of  barley,  and  five  acres  each 
of  corn  fodder,  rye,  peas,  and  potatoes,  while  20  acres 
are  reserved  for  pasture.  The  main  income  is  derived 
from  the  sale  of  live  stock  and  dairy  products. 

Problems  on  Rotations 

1.  Plan  a  rotation  for  general  fanning  ( 160  acres),  using  the  fol- 
lowing crops:  clover,  timothy,  barley,  oats,  potatoes,  and  corn.  The 
soil  is  in  an  average  state  of  fertility.  Twenty-five  head  of  stock 
are  kept. 

2.  Plan  a  three-course  rotation  for  a  sandy  soil,  the  main  object 
being  potato  culture. 

3.  Plan  a  seven-year  rotation  for  grain  farming,  using  manure 
and  sodium  nitrate  once  during  the  rotation.  The  soil  is  a  clay 
loam  in  a  good  state  of  fertility. 

4.  Plan  a  rotation  for  general  farming  on  a  sandy  loam. 

5.  How  would  you  proceed  to  bring  an  old  grain  farm  from  a  low 
to  a  high  state  of  productiveness?  Begin  with  the  feeding  of  the 
stock. 

6.  Using  conmiercial  and  special-purpose  manures,  how  would 
you  proceed  to  raise  wheat,  potatoes,  and  hay,  each  continuously? 

7.  Plan  a  rotation  for  a  northern  latitude,  where  corn  cannot  be 
grown,  and  where  clover  and  timothy  fail  to  do  well;  wheat  and  all 
small  grains  thrive  ;  also  millet,  peas,  rape,  and  some  of  the  root 
crops.  The  soil  is  a  clay  loam,  resting  on  a  marl  subsoil.  Manure 
is  very  slow  in  decomposing.  The  rotation  should  be  suited  to 
general  farming,  wheat  being  the  important  market  crop. 


CONSERVATION  OF  FERTILITY 

321.  Manures  Necessary  for  Conservation  of  Fer- 
tility. —  In  order  to  conserve  the  fertility  of  the  soil, 
not  only  must  a  systematic  rotation  be  practiced,  but 
a  proper  use  must  be  made  of  the  crops  produced. 
When  they  are  sold  from  the  farm  and  no  restoration 
is  made  soils  are  gradually  depleted  of  their  fertility. 
No  soil  has  ever  been  found  that  will  continue  to  pro- 
duce crops  without  the  use  of  manures.  Many  prairie 
soils  give  large  yields  for  long  periods  without  manur- 
ing, but  they  are  never  able  to  compete  in  productive- 
ness with  similar  soils  that  have  been  systematically 
cropped  and  manured.  With  a  fertile  soil  the  decline 
of  fertility  is  so  gradual  that  it  is  not  observed  unless 
careful  records  are  kept  of  the  3'ields  from  year  to  year. 

322.  Use  of  Crops. —  The  use  made  of  crops  whether 
as  food  for  stock  or  sold  directly  from  the  farm,  deter- 
mines the  future  crop-producing  power  of  the  soil. 
With  different  systems  of  farming  different  uses  are 
made  of  crops.  When  exclusive  grain  farming  is  fol- 
lowed no  restoration  of  fertility  is  made,  while  in  the 
case  of  stock  farming,  the  manure  produced  contains 
fertility  in  proportion  to  the  crops  consumed.  If 
good  care  is  taken  of  the  manure,  and  in  place  of  the 
grains  sold,  mill  products  are  purchased  and  fed,  there 
is  no  loss  of  fertility.  Between  these  two  extremes, 
exclusive  grain  farming  and  stock  farming,  there  are 
found  in  actual  practice,  different  systems  of  farming, 


250  SOILS    AND    FERTILIZERS 

which  remove  various  amounts  of  fertility  from  the 
soil. 

323.  Two  Systems  of  Farming  Compared. —  The 
losses  of  fertility  from  farms  are  determined  by  the 
crops  and  products  sold,  the  care  of  the  manure,  and 
the  fertility  in  the  products  purchased  and  used  on  the 
farm.  If  an  account  were  kept  of  the  income  and 
outgo  of  the  fertility  of  farms  it  would  be  found  that 
with  some  systems,  the  soil  is  gaining  in  fertility,  while 
with  others  a  rapid  decline  occurs.  In  studying  the 
income  and  outgo  of  fertility,  it  is  necessary  to  calcu- 
late the  amount  of  the  three  principal  elements,  nitro- 
gen, phosphoric  acid,  and  potash  in  the  crops  and 
products  sold.  For  making  these  calculations  tables 
are  given  in  Sections  178  and  290.  In  the  handling  of  ma- 
nure it  is  impossible  to  prevent  losses,  but  it  is  possible 
to  reduce  them  to  very  small  amounts.  Hence  in  the 
calculations,  a  loss  of  3  per  cent,  is  allowed  for  mechan- 
ical waste,  and  for  uneven  distribution  of  the  manure; 
that  is,  in  addition  to  the  fertility  sold  from  the  farm  a 
loss  of  3  per  cent,  is  allowed  for  all  crops  raised  and 
consumed  as  food  by  stock. 

On  one  farm  the  crops  raised  and  sold  are  :  Flax  40 
acres,  wheat  50  acres,  oats  20  acres,  barley  50  acres  ; 
no  stock  is  kept,  the  straw  is  burned,  and  the  ashes 
are  w^asted. 


CONSERVATION    OF    FERTILITY  25 1 

Exci^usivE  Grain  Farming. 
Sold  from  the  Farm 

Phosphoric 
Nitrogen.  acid.  Potash. 

Pounds.  Pounds.  Pounds. 

Flax,  40  acres 1600  600  800 

Flax  straw 600  120  320 

Wheat,  50  acres 1250  625  350 

Wheat  straw 500  375  1400 

Oats,  20  acres 700  240  200 

Oat  straw 300  1 20  700 

Barley,  50  acres 1400  750  400 

Barley  straw 600  250  1500 

Total 6950  3080  5670 

In  addition  to  the  nitrogen  removed  in  the  crops 
other  losses  mnst  be  considered.  Experiments  have 
shown  that  when  exchisive  grain  farming  is  practiced, 
for  every  pound  of  nitrogen  removed  in  the  crop,  four 
pounds  are  lost  from  the  soil  in  other  w^ays.  This 
w^ould  make  the  total  loss  of  nitrogen  over  28,500 
pounds  or  177  pounds  per  acre,  w-hich  large  as  it  may 
seem  is  the  actual  loss  from  the  soil  when  grain  only 
is  raised  and  sold.  Experiments  at  the  Minnesota 
Experiment  Station  have  shown  that  after  a  soil  had 
been  cultivated  40  years,  the  annual  loss  per  acre  of 
nitrogen  in  exclusive  wheat  raising  was  25  pounds 
through  the  crop  and  146  pounds  due  to  the  oxidation 
of  the  nitrogenous  humus  of  the  soil.'^ 

When  exclusive  grain  farming  is  followed,  the 
annual  losses  of  fertility  from  a  farm  of  160  acres  are 
28,500  pounds  of  nitrogen,  3000  pounds  of  phosphoric 
acid,  and  5500  pounds  of  potash. 


252  SOILS    AND    FERTILIZERS 

On  a  similar  farm  of  160  acres  the  crops  are  rotated 

as  described  in  Section  320.     The  amounts  of  fertility 

in  the   products  sold,  the  crops  raised  and  consumed 

as  fodder,  and  the  food  and  fuel  purchased,  are  given 
in  the  following  table: 

Stock    Farming 
Sold  from  the  Far  in 

Phosphoric 

Nitrogen.          acid.  Potash. 

Pounds.        Pounds.  Pounds. 

Butter,  5000  pounds 5                 5  5 

Young  cattle,  10  head 200             190  16 

Hogs,  20  of  250  pounds  each-     100              40  10 

Steers,  2 48               38  4 

Wheat,  10  acres 250             125  70 

Flax,  10  acres 390             150  190 

Rye,  10  acres 285             128  85 

Total 1278             676  380 

Raised  and  Consumed  on  the  Farm 

Clover,  20  tons 66             270  600 

Timothy.  20  tons 600             180  8cK) 

Corn,  20  acres 1500            300  800 

Corn  fodder,  i  acre 75               15  60 

Mangels,  2  acres 150               70  300 

Potatoes,  I  acre 40               20  75 

Straw,  40  tons 400             200  1000 

Peas,  5  acres 85  200 

Oats,  20  acres 700             240  200 

Barley,  20  acres  with  straw-  •     800            400  760 

4265           1780  4795 
Mechanical  loss  of   food  con- 
sumed, 3  per  cent 128               53  144 


CONSERVATION    OF    FERTILITY  253 

Food  and  Fuel  Purchased 

Phosphoric 

Nitrogen.  acid.  Potash. 

Pounds.        Pounds.       Pounds. 

Bran,  5  tons 275  260  150 

Shorts,  5  tons 250  150  100 

Oil  meal,  2  tons 100  35  25 

Hard-wood  ashes 25  100 

625  470  375 

Sold  from  farm 1278  676  380 

Ivoss  in  food  consumed,  etc  .. .      128  53  144 

Total 1406  729  524 

Food  and  fuel  purchased 625  470  375 

Balance  lost  from  farm 781  259  149 

The  manure  produced  and  used  on  this  farm  results 
in  the  production  of  larger  crop  yields  than  is  the 
case  with  exclusive  grain  culture.  The  clover  and 
peas  more  than  balance  the  loss  of  nitrogen.  Ex- 
periments have  shown  that  a  rotation  similar  to 
this  caused  an  increase  in  soil  nitrogen.  Manure, 
meadow  and  pasture  all  tend  to  increase  the  soil 
humus  and  nitrogen.  The  losses  of  phosphoric  acid 
and  potash  are  exceedingly  small,  averaging  less 
than  a  pound  per  acre  of  each.  The  action  of  manure 
on  this  farm  is  continually  bringing  into  activity  the 
inert  plant  food  of  the  soil  so  that  every  year  there  is 
a  larger  amount  of  active  plant  food,  which  results  in 
producing  larger  yields  per  acre. 

The  increase  or  decrease  of  fertility  on  farms  has 
a  marked  effect  upon  crop  yields.     For  example  the 


254  SOILS   AND   FERTILIZERS 

averagfe  yield  of  wheat  in  those  counties  in  Minnesota 
where  live  stock  is  kept,  is  7  bushels  per  acre  greater 
than  in  similar  counties  where  all  grain  farming  is 
followed. 

Problems 

Calculate  the  income  and  outgo  of  fertility  from  the  following 
farms  : 

1.  Sold  from  the  farm  :  wheat  40  acres,  oats  40  acres,  barley  40 
acres,  rye  20  acres,  flax  10  acres.  The  straw  is  burned  and  no  use 
is  made  of  any  manures. 

2.  Sold  from  the  farm  :  wheat  20  acres,  barley  20  acres,  flax  5 
acres,  1000  pounds  of  butter,  10  hogs,  and  10  steers.  Purchased  : 
Bran  3  tons,  shorts  2  tons,  oil  meal  i  ton.  Crops  produced  and  fed 
on  farm  :  Clover  and  timothy  hay  40  tons,  corn  fodder  3  acres,  corn 
10  acres,  oats  and  peas  10  acres,  roots  i  acre,  millet  i  acre,  and  bar- 
ley 5  acres. 

3.  Sold  from  the  farm  :  Wheat  10  acres,  sugar  beets  5  acres,  milk 
100,000  pounds,  butter  500  pounds,  20  pigs,  6  head  of  young  stock, 
2  acres  of  potatoes.  Purchased  :  5  tons  of  bran,  2  tons  of  oil  meal, 
T  ton  of  cottonseed  meal,  15  cords  of  wood,  i  ton  of  acid  phosphate, 
1000  pounds  of  potassium  sulphate,  and  500  pounds  of  sodium  ni- 
trate. Raised  and  consumed  on  the  farm  :  Corn  fodder  15  acres, 
mangels  i  acre,  peas  and  oats  5  acres,  clover  20  tons,  timothy  10 
tons,  straw  from  grain  sold,  oats,  10  acres,  corn  20  acres. 


REFERENCES 

1.  Venable  :  Histon*  of  Chemistry. 

2.  Gilbert  :  Inaugural  Lecture,  University  of  Oxford. 

3.  Liebig  :  Cheniistr\-   in  Its  Applications  to   Agriculture   and 
Physiology. 

4.  Gilbert:  The  Scientific  Principles  of  Agriculture  (Lecture). 

5.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  30. 

6.  Stockbridge  :  Rocks  and  Soils. 

7.  Association  of  Official  Agricultural  Chemists,  Report  1898. 
Note  :  —  This  sentence  should  read  :    A  division  has  recently 

been  suggested  by  Hopkins  in  which  the  square  root  of  ten  is 
taken  as  the  constant  ratio  between  the  grade  of  soil  particles. 

8.  Maryland  Agricultural  Experiment  Station,  Bulletin  No.  21. 

9.  Osborne  :  Journal  of  Analytical  Chemistry,  Vol.  II,  Part  3. 

10.  Wiley  :  Agricultural  Analysis,  Vol.  I. 

11.  Hellriegel  :  Calculated  from  Beitrage   zu   den  Natunvissen- 
schaft  Grandlagen  des  Ackerbaus. 

12.  King  :  Wisconsin    Agricultural  Experiment  Station,  Report 
1889. 

13.  Unpublished  results  of  author. 

14.  King  :  Soils. 

15.  Roberts  :  Fertility  of  the  Land. 

16.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  41. 

17.  Minnesota  Agricidtural  Experiment  Station,  Bulletin  No.  53. 

18.  Whitney  :  Division  of  Soils,  U.  S.  Department  of  Agriculture, 
Bulletin  No.  6. 

19.  Merrill  :  Rocks,  Rock-weathering  and  Soils. 

20.  Miintz  :  Comptes  Rendus  de  I'Acadeinie  des  Sciences,  CX 
(1890). 

21.  Storer  :  Agriculture,  Vol.  I. 

22.  Dyer  :  Journal  of  the  Chemical  Society,  March,  1894. 

23.  Goss  :  Association  of  Official  Agricultural  Chemists,  Report 
1896. 


256  SOILS   AND    FERTILIZERS 

24.  Peter  :  Association  of  Official  Agricultural  Chemists,  Report 

1895. 

25.  Loughridge  :  American  Journal  of  Science,  Vol.  VII  (1874). 

26.  Hilgard  :  Year-book  U.  S.  Department  of  Agriculture,  1895. 

27.  Houston  :  Indiana  Agricultural  Experiment  Stalion,  Bulle- 
tin No.  46. 

28.  Miilder  :  From  Mayer  :  Lehrbuch  der  Agrikulturchemie,  2. 

29.  Journal  of  the  American  Chemical  Society,  Vol.  XIX,  No.  9. 

30.  Year-book  U.  S.  Department  Agriculture,  1895. 

31.  Loughridge  :  South  Carolina  Agricultural    Experiment  Sta- 
tion, Second  Annual  Report. 

32.  Association  of  Official  Agricultural  Chemists,  Report  1893. 

33.  Washington  Agricultural  Experiment  Station,   Bulletin  No. 

13- 

34.  Association  of  Official  Agricultural  Chemists,  Report  1894. 

35.  California  Agricultural  Experiment  Station,  Report  1890. 

36.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  29. 

37.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  47. 

38.  Lawes  and  Gilbert  :  Experiments  on  Vegetation,  Vol.  I. 

39.  Boussingault  :  Agronomic,  Tome  I. 

40.  Atwater :  American  Chemical  Journal,  Vol.  VI,   No.   8  and 
Vol.  VIII,  No.  5. 

41.  Hellriegel  :  Welche  Stick stofF  Quellen  stehen  der  Pflanze  zu 
Gebote? 

42.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  34. 

43.  Warington  :  U.  S.  Department  of  Agriculture,  Office  of  Ex- 
periment Stations,  Bulletin  No.  8. 

44.  Hilgard  :  Association  of  Official  Agricultural  Chemists,  Re- 
port 1895. 

45.  Marchal  :  Journal  of  the  Chemical  Society  (abstract),  June, 
1894. 

46.  Kiinnemann:  Die  Landwirthschaftlichen  Versuchs-Stationen, 
50(1898). 

47.  Adametz :  Abstract,  Biedermann's  Centralblatt  fiir  Agrikul- 
turchemie,  1887. 

48.  Atwater:  American  Chemical  Journal,  Vol.  IX  (1887). 


REFERENCES  257 

49.  Stutzer  :  Biedermann's  Centralblatt  fiir  Agriciilturchemie, 
1883. 

50.  Jenkins  :  Connecticut  State  Agricultural  Experiment  Sta- 
tion, Report  1893. 

51.  Wagner  :  Biedermann's  Centralblatt  fiir  Agrikulturchemie, 
1897. 

52.  Journal  of  the  Royal  Agricultural  Society,  1850. 

53.  From  Sachsse  :  Lehrbuch  der  Agrikulturchemie. 

54.  Lawes  and  Gilbert  :  Experiments  with  Animals. 

55.  Beal  :  U.  S.  Department  of  Agriculture,  Farmers'  Bulletin 
No.  21. 

56.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  26. 

57.  Mainly  from  Armsby  :  Pennsylvania  Agricultural  Experi- 
ment Station,  Report  1890.  Figures  for  grains  calculated  from 
original  data. 

58.  Heiden  :  Dungelehre. 

59.  Liebig  :  Natural  Laws  of  Husbandry. 

60.  Cornell  University  Agricultural  Experiment  Station,  Bulle- 
tins Nos.  13,  27,  and  56. 

61.  Kinnard  :  From  Manures  and  Manuring  by  Aikman. 

62.  Wyatt :  Phosphates  of  America. 

63.  Wiley  :  Agricultural  Analysis,  Vol.  III. 

64.  Goessmann  :  Massachusetts  Agricultural  Experiment  Station, 
Report  1894. 

65.  Connecticut  (State)  Agricultural  Experiment  Station,  Bulle- 
tin No.  103. 

66.  Goessmann:  Massachusetts  Agricultural  Experiment  Station, 
Report  1896. 

67.  Wheeler  :  Rhode  Island  Agricultural  Experiment  Station, 
Reports  1892,  1893,  etc. 

68.  Boussingault  :  From  Storer :  Agriculture. 

69.  Handbook  of  Experiment  Station  Work. 

70.  New  York  (State)  Agricultural  Experiment  Station,  Bulle- 
tin No.  108. 

71.  Voorhees  :  U.  S.  Department  of  Agriculture,  Farmers'  Bulletin 
No.  44. 


258  SOILS   AND    FERTILIZERS 

72.  Liebig  :  Die   Chemie   in   ihrer   Anwendung   auf   Agrikultur 
und  Physiologic. 

73.  Warington  :  Chemistry  of  the  Farm. 

74.  Lawes  and  Gilbert  :  Growth  of  Wheat. 

75.  Lawes  and  Gilbert  :  Growth  of  Barley. 

76.  Lugger  :  Minnesota  Agricultural  Experiment  Station,  Bulle- 
tin No.  13. 

77.  Lawes  and  Gilbert  :  Growth  of  Potatoes, 

78.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  56. 

79.  Shaw  :  L^.  vS.   Department  of  Agriculture,  Farmers'  Bulletin 
No.  II. 

80.  White  :  U.  S.  Department  of  Agriculture,  Farmers'  Bulletin 
No.  48. 

81.  Lawes  and  Gilbert  :  Permanent  Meadows. 

82.  Thompson  :  Graduating  Essay,  Minnesota  School  of  Agricul- 
ture. 

83.  Nefedor  :  Abstract,  Experiment  Station  Record,  Vol.  X,  No.  4. 


EXPERIMENTS 

1.  Pulverized  Rock  and  Soil.  —  Pulverize  in  an  iron  mortar, 
pieces  of  feldspar,  mica,  granite,  and  limestone.  Examine  each 
with  a  lens.  Finally  mix  all  of  the  pulverized  material,  and  com- 
pare the  mixture  with  samples  of  soil. 

2.  Weight  of  Soils.  —  Weigh  a  cubic  foot  of  air-dried  sand,  clay, 
and  peat.  For  this  purpose  use  a  box  holding  ^  of  a  cubic  foot  of 
soil.     Do  not  compact  the  soil. 

3.  Form  of  Soil  Particles.  —  Examine  under  a  microscope  soil 
particles  and  distinguish  the  various  grades  of  sand  and  silt.  Ob- 
serve the  form  of  the  soil  particles  and  make  drawings  of  them. 

4.  Separation  of  Soil  Particles.  — By  means  of  sieves,  with  holes, 
I,  ^,  and  %  mm.  in  diameter,  separate  these  three  grades  of  parti- 
cles as  described  in  Section  10.  To  what  type  does  the  soil 
examined  belong? 

5.  Capillarity.  —  Place  small  glass  tubes  of  various  sizes  in  a 
vessel  of  water  and  note  the  height  to  which  water  rises  by  capil- 
larity. 

6.  Capillarity  of  Soils.  —  Fill  glass  tubes  2  inches  in  diameter 
w4th  clay  and  fine  sand,  respectively.  Support  the  tubes  so  that 
one  end  will  touch  the  water  in  a  cylinder.  Observe  the  rate  and 
height  to  which  the  capillary  water  rises,  making  daily  measure- 
ments for  a  week. 

7.  Hydroscopic  Moisture.  —  Places  grams  of  air-dried  soil  on  a 
watch-glass,  in  a  water-oven,  and  after  two  hours  reweigh  and  de- 
termine the  loss  of  weight.  Calculate  the  per  cent,  of  hydroscopic 
moisture. 

8.  Influence  of  Cultivation  on  Soil  Water.  —  Fill  four  boxes,  each 
a  foot  square  and  a  foot  deep,  with  air-dried  loam  soil.  Weigh  the 
boxes  and  soil  used.  Each  box  is  to  be  treated  separately  as  fol- 
lows :  Measure  one-half  gallon  of  water  into  a  watering-pot.  Allow 
the  water  from  the  watering-pot  to  flow  on  the  soil,  regulating  the 
flow  so  that  it  is  all  absorbed.     The  soil  should  be  saturated,  but 


26o  SOILS    AND    FERTILIZERS 

there  should  be  no  dripping.  Measure  or  weigh  any  water  left  in 
the  watering-pot.  One  box  is  to  receive  shallow  surface  cultivation, 
using  for  the  purpose  a  small  gardener's  tool.  Another  box  is  to 
be  left  without  receiving  any  treatment.  The  third  is  to  receive 
treatment  imitating  that  of  the  disk  harrow,  having  the  disks  set  per- 
pendicularly. A  sharj)  knife  may  be  used  for  this  purpose.  In  the 
fourth  box  the  disk  cuttings  are  to  be  made  at  an  angle.  Leave 
each  box  exposed  to  the  sun  or  in  a  heated  room,  and  determine 
the  loss  of  weight  every  day  for  a  week.  From  the  loss  of  weight, 
determine  the  per  cent,  of  water  lost  and  the  per  cent,  left  in  the 
soil. 

9.  Capacity  of  Soil  to  Absorb  Water.  —  Weigh  100  grams  of  dry 
soil.  Fit  a  medium-sized  filter-paper  in  a  funnel.  Moisten  the 
paper  so  that  it  will  not  absorb  an}-  more  water.  Then  place  the 
soil  in  the  filter  and  add  slowly  from  a  beaker,  containing  exactly 
100  cc.  of  water,  enough  to  thoroughly  saturate  the  soil.  Collect 
all  of  the  drippings  from  the  funnel.  Measvire  the  drippings  and 
the  unused  water  in  the  beaker.  Calculate  the  per  cent,  of  water 
absorbed  b\-  the  soil. 

10.  Capacity  of  Sand  for  Holding  Water.  —  Repeat  Experiment  9, 
using  sand. 

11.  The  Influence  of  Manure  upon  the  Water-holding  Power  of 
Soil.  — Repeat  Experiment  9,  using  95  grams  of  sand  and  5  grams 
of  dry  and  finely  pulverized  manure.  The  sand  and  manure 
should  be  thoroughly  mixed  before  performing  the  experiment. 

12.  Action  of  Heat  upon  Soils.  —  Expose  to  the  sun's  rays  samples 
of  dry  clay,  peat,  and  sand ;  after  two  hours'  exposure,  obtain  the 
temperature  of  each.  The  bulb  of  the  thermometer  is  simply  cov- 
ered with  soil.  All  of  the  observations  should  be  made  under  sim- 
ilar conditions. 

13.  Influence  of  Manure  upon  Soil  Temperature. —  Expose  to  the 
sun's  rays,  moist  clay  soil,  and  mixed  cla3'and  fresh  horse  manure. 
After  two  hours  observe  the  temperature  of  each. 

14.  Odor  and  Taste  of  Soils.  —  Observe  the  odor  of  dry,  peaty 
soil    that    has  been    kept  in  a  corked  bottle.     Note  the   taste  of 


EXPERIMENTS 


261 


peaty  and  of  alkaline  soils  ;  test  each  wdth  moistened  litmus  paper. 

15.  Absorption  of  Gases.  —  Put  50  grams  of  soil  into  a  wide- 
mouthed  bottle,  add  50  cc.  of  water  and  i  cc.  strong  ammonia. 
Note  the  odor.  Cork  the  bottle,  shake,  and  after  twenty-fqur 
hours  again  observe  the  odor. 

16.  Insoluble  and  Soluble  Products  of  Soil.  —  Digest  in  a  covered 
beaker  10  grams  of  soil  with  100  cc.  hydrochloric  acid  (50  cc. 
strong  hydrochloric  acid  and  50  cc.  water).  After  two  hours'  diges- 
tion, cool  and  filter,  using  25  cc.  water  to  wash  the  acid  from  the 
insoluble  residue.  Note  the  quantity  and  appearance  of  the  insol- 
uble matter.  To  one-half  the  filtrate  add  ammonia  until  alkaline. 
What  is  the  precipitate  ?  Remove  it  by  filtering,  and  to  this  second 
filtrate  add  ammonium  oxalate.  What  is  the  precipitate  ? 
Evaporate  the  remainder  of  the  original  filtrate  nearly  to 
dryness.  Add  20  cc.  water,  3  cc.  nitric  acid,  and  5  cc.  of 
ammonium  molybdate.  After  shaking  the  test-tube  con- 
taining the  mixture,  it  is  placed  in  a  beaker  of  water  and 
heated  to  about  65°  C.      W^hat  is  the  yellow  precipitate  ? 

17.  Testing  Soils  for  Combined  Carbon  Dioxide. — One 
gram  of  soil  is  placed  in  a  test-tube  (Fig.  35)  and  5  cc.  of 
water  and  3  cc.  of  hydrochloric  acid  added.  A  small 
looped  tube  a,  containing  a  drop  of  lime-water,  is  then 
inserted  into  the  test-tube.  The  test-tube  is  warmed. 
Observe  the  precipitate  formed  in  the  loop.     What  is  it  ? 

18.  Humus  from  Soils.  — Five  grams  of  soil  are  placed 
in  a  glass-stoppered  bottle,  100  cc.  water  and  3  cc.  hydro- 
chloric acid  added.     After   shaking,    the  contents  of  the 
bottle   are   left  twenty-four  hours  to  subside.     The  acid 
is  then  poured  off  and  100  cc.   of  water  added.     The  soil 
is  left  until  the  next  day,  when  the  water  is  poured  off  and   V^__^/ 
100  cc.  of  water  and  5  cc.  of  ammonia  are   added.     After     Fig-  35- 
shaking  and  allowing  a  little  time  for  the  soil  to  settle,  the  ammo- 
nia solution  is  filtered  off. 

To  a  portion  of  the  filtrate  add  hydrochloric  acid  until  the  solu- 
tion is  just  acid.  Observe  the  precipitate.  Evaporate  another  por- 
tion of  the  solution  to  drvness.     What  is  the  black  residue  ? 


a 


6 


262  SOILS    AND    FERTILIZERS 

19.  The  nitrogen  of  soils.  —  Place  in  a  strong  test-tube  a  mixture 
of  5  grams  of  soil  and  an  equal  bulk  of  soda-lime.  Connect  the 
test-tube  wdth  a  delivery-tube  which  leads  into  another  test-tube 
containing  distilled  water.  Heat  the  test-tube  containing  the  soil  for 
five  or  ten  minutes.  Then  test  with  litmus  paper  the  liquid  in  the 
second  test-tube,  neutralize  with  standard  acid  as  in  Experiment  30. 

20.  Nitrates.  —  Examine  laboratory  samples  of  the  following 
nitrates:  Potassium,  calcium,  and  sodium.  Place  in  separate  test- 
tubes  Yz  gram  of  each,  add  10  cc.  of  water,  and  heat  gently.  To 
each  when  cool  add  a  few  drops  of  sulphuric  acid,  then  a  few  drops 
of  an  indigo  solution. 

21.  The  Nitrogen  of  Blood.  —  Repeat  Experiment  19,  using  100 
milligrams  of  dried  blood  in  place  of  the  soil. 

22.  Organic  Nitrogen  Soluble  in  Pepsin.  —  Prepare  a  pepsin  solu- 
tion by  dissolving  5  grams  of  commercial  pepsin  in  a  liter  of  water, 
adding  i  cc.  of  strong  hydrochloric  acid.  Place  in  separate  test- 
tubes  5  grams  each  of  dried  blood,  tankage,  and  horn  meal.  Add 
25  cc.  of  pepsin  solution  and  place  the  test-tubes  in  a  cylinder  con- 
taining water  at  a  temperature  of  40°  C.  Shake  the  test-tubes  occa- 
sionally, and  at  the  end  of  one-,  two-,  and  five-hour  periods  observe 
the  amounts  of  insoluble  matter  remaining  in  the  test-tubes. 

23.  Testing  for  Nitrates.  —  Dissolve  some  sodium  nitrate,  not 
exceeding  100  milligrams,  in  10  cc.  water.  Add  2  cc.  of  a  dilute 
solution  of  ferrous  sulphate,  and  place  the  test-tube  in  a  cylinder 
of  water.  Sulphuric  acid  is  then  added  by  means  of  a  long  stemmed 
funnel.     Observe  the  dark  ring  formed. 

24.  Water  in  Manure.  —  Dr}'  100  grams  of  fresh  manure  in  a 
water-oven  for  four  hours.  Determine  the  loss  of  weight  and  the 
per  cent,  of  water. 

25.  Leaching  Manure.  —  Place  5  kilos  of  manure,  the  same  as 
used  in  Pixperiment  24,  in  a  box  provided  with  small  holes  in  the 
bottom,  so  that  the  manure  can  be  leached.  Place  the  box  over  a 
sink  or  a  receptacle  for  receiving  the  leachings.  Percolate  3  gallons 
of  water  through  the  manure,  daily,  for  five  days.  Finally  weigh 
the  manure,  determine  the  per  cent,  of  water,  and  the  total  loss  of 
dry  matter. 


EXPERIMENTS  263 

26.  Volatilizing  Ammonium  Salts. — In  separate  test-tubes  place 
about  100  milligrams  each  of  ammonium  carbonate  and  ammonium 
sulphate.  Apply  heat  gently  and  observe  the  results.  Place  a  cold 
glass  rod  in  the  test-tube  when  the  white  fumes  are  being  given  off. 

27.  Testing  for  Phosphoric  Acid.  —  Dissolve  a  small  piece  of  bone 
(5  grams)  in  20  cc.  nitric  acid  (10  cc.  strong  nitric  acid  and  10  cc. 
water).  Filter.  To  the  filtrate  add  3  cc.  of  ammonium  molybdate, 
warm,  and  shake.  In  a  second  test-tube  dissolve  100  milligrams  of 
sodium  phosphate  in  10  cc.  water  and  add  3  cc.  ammonium  mo- 
lybdate.    Compare  the  result  with  that  obtained  with  the  bone. 

28.  Testing  for  Water-soluble  and  Acid-soluble  Phosphates.  — 
Place  I  gram  of  tricalcium  phosphate  in  a  test-tube  with  10  cc. 
water.  Boil.  Filter  through  a  close  filter.  To  the  filtrate  add  3  cc. 
of  ammonium  molybdate.  Repeat  the  experiment,  using  dilute 
nitric  acid  in  place  of  water.  Repeat  the  experiment,  using  mono- 
calcium  phosphate  and  water. 

29.  Preparation  of  Acid  Phosphate. — Place  100  grams  of  pow- 
dered tricalcium  phosphate  in  a  large  lead  dish.  Add  slowly  and 
with  constant  stirring  100  grams  of  commercial  sulphuric  acid, 
using  an  iron  spatula  for  the  purpose.  Transfer  the  mixture  to  a 
wooden  box  and  allow  it  to  act  for  about  three  days.  Then  pul- 
verize and  examine.  The  material  is  saved  for  Experiment  34. 
The  mixing  of  the  acid  and  phosphate  should  be  Hone  in  a  place 
where  there  is  a  good  draft. 

30.  Testing  Ashes.  —  Test  samples  of  leached  and  of  unleached 
ashes  in  the  way  described  in  Section  240. 

31.  Flocculation  of  Clay. —  Ten  grams  of  clay  soil  are  placed  in 
a  tall  beaker  or  cylinder,  1000  cc.  of  water  added,  and  the  material 
triturated.  The  water  containing  the  suspended  clay  is  divided 
into  two  portions.  To  one  portion  i  gram  of  calcium  carbonate  is 
added  and  the  mixture  stirred.  After  two  or  three  hours  compare 
the  two  portions. 

32.  Action  of  Lime  on  Acid  Soil.  —  In  a  flask  place  100  grams 
of  acid  peaty  soil,  add  5  grams  of  recently  slaked  lime  and  200  cc. 
water  ;  connect  the  flask  by  means  of  a  delivery-tube  with  a  wash- 
bottle  containing  lime-water  and  observe  the  results. 


264  SOILS   AND    FERTILIZERS 

33.  Mad. — Test  a  sample  of  marl  for  lime  and  carbon  dioxide, 
as  directed  in  Experiments  16  and  17.  Observe  the  nature  of  the 
insoluble  residue.     Test  the  marl  with  litnms  paper. 

34.  Testing  Land  Plaster.  —  Test  for  carbon  dioxide  as  directed 
in  Experiment  17.  There  should  be  but  little  carbon  dioxide  in 
the  best  grades  of  land  plaster.  Digest  i  gram  of  gypsum  in  a  test- 
tube  with  10  cc.  dilute  hydrochloric  acid.  Observe  the  nature  and 
the  amount  of  insoluble  matter. 

35.  Mixing  Fertilizers. —  Mix  in  a  large  box 

200  grams  acid  phosphate  (saved  from  28), 
50  grams  kainit, 
50  grams  sodium  nitrate. 
Calculate  the  approximate  composition  of  this  fertilizer  and  its 
trade  value. 

36.  Testing  Fertilizers. — Test  the  above  fertilizer  for  water- 
soluble  phosphoric  acid,  as  directed  in  Experiment  27.  Test  for 
nitrogen  pentoxide,  as  directed  in  Experiment  19. 

37.  Calculating  Results.  —  A  fertilizer  is  said  to  contain  3.1  per 
cent,  ammonia,  12  per  cent,  bone  phosphate  of  lime  and  6  per  cent, 
potassium  sulphate  ;  calculate  the  equivalent  amounts  of  nitrogen, 
phosphoric  acid,  and  potash. 


REVIEW  QUESTIONS 

I.  From  what  are  soils  derived  ?  2.  What  are  the  physical  prop- 
erties of  soils  ?  3.  Why  do  soils  differ  in  weight?  Arrange  clay, 
sand,  loam,  and  peat  in  order  of  weight  per  cubic  foot.  4.  When 
wet,  what  would  be  the  order  ?  5.  What  is  the  absolute  and  what  the 
apparent  specific  gravity  of  soils  ?  6.  Define  the  terms  :  Skeleton,  fine 
earth,  fine  sand,  silt,  and  clay.  7.  What  are  the  physical  properties 
of  clay  ?  8.  What  are  the  forms  of  the  soil  particles  ?  9.  How  do 
different  t3'pes  of  soil  vary  as  to  the  number  of  soil  particles  per 
gram  of  soil  ?     10.  How  is  a  mechanical  analysis  of  a  soil  made  ? 

11.  Why  do  certain  crops  thrive  best  on   definite  types   of  soil? 

12.  W^hat  factors  must  be  taken  into  consideration  in  determining 
the  type  to  which  a  soil  belongs  ?  13.  Explain  the  mechanical 
structure  of  a  good  potato  soil.  14.  How  does  a  wheat  soil  differ  in 
mechanical  structure  from  a  truck  soil?  15.  A  good  corn  soil  is 
also  a  good  type  for  what  other  crops?  16.  How  much  water  is  re- 
quired to  produce  an  average  grain  crop,  and  how  do  the  rainfall 
and  the  water  removed  in  crops  during  the  growing  season  compare  ? 
17.  In  what  forms  may  water  be  present  in  soils  ?  18.  What  is  bot- 
tom water  and  when  may  it  be  utilized  by  crops  ?  19.  What  is  capil- 
lary water?  20.  Explain  the  capillar}' movement  of  water.  21.  Ex- 
plain how  the  capillary  and  non-capillary  spaces  in  the  soil  ma}-  be 
influenced  by  cultivation.  22.  What  is  hydroscopic  w^ater  and  of 
what  value  is  it  to  crops  ?  23.  What  is  percolation  ?  24.  To  what 
extent  may  losses  occur  by  percolation  ?  25.  What  are  the  factors 
which  influence  evaporation  ?  26.  What  is  transpiration  ?  27.  In 
what  three  ways  may  water  be  lost  from  the  soil  ?  28.  Why  does 
shallow  surface  cultivation  prevent  evaporation  ?  29.  Why  is  it 
necessary  to  cultivate  the  soil  after  a  rain  ?  30.  Explain  the  move- 
ment of  the  soil  water  after  a  light  shower.  31.  What  influence 
has  rolling  the  land  upon  the  moisture  content  of  the  soil  ?  32. 
What  is  subsoiling  and  how  does  it  influence  the  moisture  content 
of  soils  ?  33.  What  influence  does  early  spring  plowing  exert  upon 
the  soil  moisture?  34.  What  is  the  action  of  a  mulch  upon  the  soil? 
35.  Why  should  different  soils  be  plowed  to  different  depths?  36.  What 
is  meant  by  the  permeability  of  a  soil  ?  37.  How  may  cultivation 
influence  permeability?  38.  How  may  commercial  fertilizers  influ- 
ence the  water  content  of  soils  ?  39.  Explain  the  physical  action 
of  well-prepared  farm  manures  upon  the  soil  and  their  influence 
upon  the  soil  water.  40.  What  is  the  object  of  good  drainage  ? 
41.  Why  does  deforesting  a  region  unfavorably  influence  the  agri- 
cultural value  of  a  country  ?  42.  What  are  the  sources  of  heat  in 
soils  ?     43.  To  what  extent  does  the  color  of  soils  influence  the  tem- 


266  SOILS   AND    FERTILIZERS 

perature  ?  44.  What  is  the  specific  heat  of  soils  ?  45.  To  what  ex- 
tent does  drainage  influence  soil  temperature  ?  46.  How  do 
manured  and  unmanured  land  compare  as  to  temperature  ?  47. 
What  relation  does  heat  bear  to  crop  growth  ?  48.  What  materials 
impart  color  to  soils?  49.  What  is  the  effect  of  loss  of  organic 
matter  upon  the  color  of  soils  ?  50.  What  materials  impart  taste  to 
soils?  Odor?  51.  What  effect  does  a  weak  current  of  electricity 
have  upon  crop  growth  ?  52.  Do  all  soils  possess  the  same  power 
to  absorb  gases?  Why?  53.  What  is  agricultural  geology?  54. 
What  agencies  have  taken  part  in  soil  formation?  55,  How  does 
the  action  of  heat  and  cold  aid  in  soil  formation?  56.  Explain  the 
action  of  water  in  soil  formation.  57.  What  is  glacial  action,  and 
how  has  it  been  an  important  factor  in  soil  formation?  58.  Ex- 
plain the  action  of  vegetation  upon  soils.  59.  How  has  the  action 
of  micro-organisms  aided  in  soil  formation  ?  60.  Explain  the 
terms  :  Sedentary,  transported,  alluvial,  colluvial,  volcanic,  and 
windformed  soils.  61.  What  is  feldspar  and  what  kind  of  soil 
does  it  produce  ?  62.  Give  the  general  composition  of  the  follow- 
ing rocks  and  minerals  and  state  the  quality  of  soil  which  each 
produces:  Granite,  mica,  hornblende,  zeolites,  kaolin,  apatite,  and 
limestone.  63.  What  elements  are  liable  to  be  the  most  deficient 
in  soils  ?  64.  Name  the  acid-  and  base-forming  elements  present 
in  soils.  65.  What  are  the  elements  most  essential  for  crop  growth  ? 
66.  State  some  of  the  different  wa^-s  in  which  the  elements  present 
in  soils  combine.  67.  Why  is  it  customary  to  speak  of  the  oxides  of 
the  elements  and  to  deal  with  them  rather  than  with  the  elements  ? 
68.  Do  the  elements  exist  in  the  soil  in  the  form  of  oxides?  69. 
What  are  double  silicates  ?  70.  In  what  forms  does  carbon  occur 
in  soils?  71.  Is  the  soil  carbon  the  source  of  the  plant  carbon  ? 
72.  What  can  you  say  regarding  the  occurrence  and  importance  of 
the  sulphur  compounds  ?  73.  What  influence  would  o.  10  per  cent, 
chlorine  have  upon  the  soil?  74.  In  what  forms  does  phosphorus 
occur  in  soils?  75.  What  is  the  principal  form  in  which  the  nitro- 
gen occurs  in  soils  ?  76.  What  can  be  said  regarding  the  hydrogen 
and  oxygen  of  the  soil?  77.  State  the  principal  forms  and  the 
value  as  plant  food  of  the  following  elements  :  Aluminum,  potas- 
sium, calcium,  sodium,  and  iron.  78.  For  plant  food  purposes, 
what  three  divisions  are  made  of  the  soil  compounds  ?  79.  Why 
are  the  complex  silicates  of  no  value  as  plant  food  ?  80.  Give  the 
relative  amounts  of  plant  food  in  the  three  classes.  81.  How  is  a 
soil  analysis  made  ?  82.  What  can  be  said  regarding  the  economic 
value  of  a  soil  analysis  ?  83.  What  are  some  of  the  important  facts 
to  observe  in  interpreting  results  of  soil  analysis  ?  84.  Under  what 
conditions  are  the  results  most  valuable  ?  85.  Do  the  terms  volatile 
matter  and  organic  matter  mean  the  same  ?     86.  How  may  organic 


REVIEW   QUESTIONS  267 

acids  be  employed  in  soil  analysis  ?  87.  Why  are  dilute  organic 
acids  used  ?  88.  Is  the  plant  food  equally  distributed  in  both  surface 
and  subsoil  ?  89.  Do  different  grades  of  soil  particles,  from  the 
same  soil,  have  the  same  composition?  90.  What  are  "alkali 
soils"?  91.  Why  is  the  alkali  sometimes  in  the  form  of  a  crust? 
92.  Are  all  soils  with  white  coating  strongly  alkaline?  93.  Give 
the  treatment  for  improving  an  alkali  soil.  94.  How  may  a  small 
"  alkali  spot  "  be  treated?  95.  What  are  the  sources  of  the  organic 
compounds  of  soils?  96.  How  may  the  organic  compounds  of  the 
soil  be  classified  ?  97.  Explain  the  term  humus.  98.  How  is  the 
humus  of  the  soil  obtained  ?  99.  W^hat  is  humification  ?  What  is 
a  humate  ?  How  are  humates  produced  in  the  soil  ?  100.  Explain 
how  different  materials  produce  humates  of  different  value.  loi. 
Arrange  in  order  of  agricultural  value  the  humates  produced  from 
the  following  materials  :  Oat  straw,  sawdust,  meat  scraps,  sugar, 
clover.  102.  Of  what  value  are  the  humates  as  plant  food  ?  103. 
How  much  plant  food  is  present  in  soils  in  humate  forms?  104. 
What  agencies  cause  a  decrease  of  the  humus  content  of  soils  ? 
105.  To  what  extent  does  humus  influence  the  physical  properties  of 
soils?  106.  What  is  humic  acid  ?  107.  What  soils  are  most  liable 
to  be  in  need  of  humus  ?  When  are  soils  not  in  need  of  humus  ? 
108.  In  what  ways  does  the  humus  of  long-cultivated  soils  differ 
from  that  of  new  soils  ?  109.  How  may  different  methods  of 
farming  influence  the  humus  content  of  soils  ?  no.  What  may  be 
said  regarding  the  importance  of  nitrogen  as  plant  food?  in. 
W^hat  are  the  functions  of  nitrogen  in  plant  nutrition?  112.  How 
may  the  foliage  indicate  a  lack  or  an  excess  of  this  element  ?  113. 
In  what  three  ways  did  Boussingault  conduct  experiments  relating 
to  the  assimilation  of  the  free  nitrogen  of  the  air?  114.  What  were 
his  results  ?  115.  What  conclusions  did  Ville  reach?  116.  Give 
the  results  of  Lawes  and  Gilbert's  experiments.  117.  How  did 
field  results  compare  with  laboratory  experiments?  118.  In  what 
ways  were  the  conditions  of  field  experiments  different  from  those 
conducted  in  the  laboratory?  119.  Give  the  results  of  Hellriegel's 
and  Wilfarth's  experiments.  120.  What  is  noticeable  regarding 
the  composition  of  clover  root  nodules  ?  121.  Of  what  agricultural 
value  are  the  results  of  Hellriegel  ?  122.  What  is  the  source  of  the 
soil's  nitrogen  ?  123.  How  may  the  organic  nitrogen  compounds 
of  the  soil  vary  as  to  complexity  ?  124.  To  what  extent  may  the 
nitrogen  in  soils  var>^  ?  125.  To  what  extent  is  nitrogen  removed 
in  crops  ?  126.  To  what  extent  are  nitrates,  nitrites,  and  ammo- 
nium compounds  found  in  soils?  127.  To  what  extent  is  nitrogen 
returned  to  the  soil  in  rain-water.  128.  How  may  the  ratio  of 
nitrogen  to  carbon  vary  in  soils  ?  Of  what  agricultural  value  is  this 
ratio?  129.  Under  what  conditions  do  soils  gain  in  nitrogen  con- 
tent?    130.  What  methods  of  cultivation  cause  the  most  rapid  de- 


268  SOILS   AND    FERTILIZERS 

cline  in  the  nitrogen  content  of  soils?  131.  What  is  nitrification? 
132.  What  are  the  conditions  necessary-  for  nitrification?  and 
what  are  the  food  requirements  of  the  nitrifying  organism?  133. 
Why  is  oxygen  necessary  for  nitrification  ?  134.  How  does  tem- 
perature, moisture,  and  sunHght  influence  this  process?  135. 
What  part  does  calcium  carbonate  and  other  basic  compounds  take 
in  nitrification  ?  136.  How  is  nitrous  acid  produced?  137.  What 
is  denitrification  ?  138.  What  other  organisms  are  present  in  soils 
besides  those  which  produce  nitrogen  pentoxide,  nitrogen  trioxide, 
and  ammonia?  139.  What  chemical  products  do  these  various  or- 
ganisms produce  ?  140.  Why  are  soils  sometimes  inoculated  with 
organisms?  141.  Why  does  summer  fallowing  of  rich  lands  cause 
a  loss  of  nitrogen?  142.  What  influence  have  deep  and  shallow 
plowing,  and  spring  and  fall  plowing  upon  the  available  soil 
nitrogen  ?  143.  Into  what  three  clavSses  are  nitrogenous  fertilizers 
divided?  14.4.  How  is  dried  blood  obtained ?  What  is  its  compo- 
sition, and  how  is  it  used?  145.  What  is  tankage?  How  is  it 
used,  and  how  does  it  differ  in  composition  from  dried  blood  ? 
146.  What  is  flesh  meal  ?  147.  What  is  fish  scrap  fertilizer,  and 
what  is  its  comparative  value  ?  148.  What  seed  residues  are  used 
as  fertilizer  ?  What  is  their  value  ?  149.  What  method  is  em- 
ployed to  detect  the  presence  of  leather,  hair,  and  wool  waste  in 
fertilizers?  Why  are  these  materials  objectionable?  150.  How 
may  peat  and  muck  be  used  as  fertilizers?  151.  What  is  sodium 
nitrate  ?  How  is  it  used,  and  what  is  its  value  as  a  fertilizer?  152. 
How  does  ammonium  sulphate,  as  a  fertilizer,  compare  in  value 
with  nitrate  of  soda  ?  153.  What  is  the  difference  between  the 
nitrogen  content  and  the  ammonia  content  of  fertilizers?  154. 
What  is  fixation  ?  Give  an  illustration.  155.  To  what  is  fixation 
due?  156.  What  part  does  liunnis  take  in  fixation  ?  157.  Why  do 
soils  differ  in  fixative  power  ?  Why  are  nitrates  not  fixed?  158. 
Why  is  fixation  a  desirable  property  of  soils?  159.  Why  is  it 
necessary  to  study  the  subject  of  fixation  in  the  use  of  manures  ? 
160.  Why  are  farm  manures  variable  in  composition?  161.  What 
is  the  distinction  between  the  terms  stable  manure  and  farm-yard 
manure?  162.  About  what  ])er  cent,  of  nitrogen,  phosphoric  acid, 
and  potash  is  present  in  ordinary  manure?  163.  Coarse  fodders 
cause  an  increase  of  what  element  in  the  manure?  164.  What  four 
factors  influence  the  composition  and  value  of  manure?  165. 
What  influence  do  absorbents  have  upon  the  composition  of 
manures?  166.  What  advantages  result  from  the  use  of  peat  and 
muck  as  absorbents?  167.  Compare  the  value  of  manure  produced 
from'clover  with  that  from  timothy  hay.  168.  How  may  the  value  of 
manure  be  determined  from  the  nature  of  the  food  consumed  ? 
169.  To  what  extent  is  the  fertility  of  the  food  returned  in  the 
manure?     170.   Is  much  nitrogen  added   to  the   body    during  the 


REVIEW    QUESTIONS  269 

process  of  fattening?  171.  Explain  the  course  of  the  nitrogen  of 
the  food  during  digestion  and  the  forms  in  which  it  is  voided  in 
the  manure.  172.  Compare  the  solid  and  liquid  excrements  as  to 
constancy  of  composition  and  amounts  produced.  173.  What  is 
meant  by  the  manurial  value  of  food  ?  174.  Name  five  foods  with 
high  manvirial  values;  also  five  with  low  manurial  values.  175. 
What  is  the  usual  commercial  value  of  manures  compared  vnth 
commercial  fertilizers?  176.  How  does  the  manure  from  young 
and  from  old  animals  compare  as  to  value?  177.  How  much 
manure  does  a  well-fed  cow  produce  per  day?  178.  What  are  the 
characteristics  of  cow  manure?  How  do  horse  manure  and  cow 
manure  differ  as  to  composition,  character,  and  fermentability ? 
179.  What  are  the  characteristics  of  sheep  manure?  180.  How 
does  hen  manure  differ  from  any  other  manure  ?  181.  Why  should 
the  solid  and  liquid  excrements  be  mixed  to  produce  balanced 
manure?  182.  What  volatile  nitrogen  compound  may  be  given  off 
from  manure  ?  183.  What  may  be  said  regarding  the  use  of  humar- 
excrements  as  manure  ?  184.  Is  there  any  danger  of  an  immediate 
scarcity  of  plant  food  to  necessitate  the  use  of  human  excrements 
as  manure  ?  185.  To  what  extent  may  losses  occur  when  manures 
are  exposed  in  loose  piles  and  allowed  to  leach  for  six  months  ? 
186.  What  two  classes  of  ferments  are  present  in  manure?  187. 
Explain  the  workings  of  the  two  classes  of  ferments  found  in 
manures.  188.  How  much  heat  may  be  produced  in  manure  dur- 
ing fermentation  ?  189.  Is  water  injurious  to  manure?  190.  How 
should  manure  be  composted  ?  What  is  gained?  191.  How  does 
properly  composted  manure  compare  in  composition  with  fresh 
manure?  192.  Explain  the  action  of  calcium  sulphate  in  the  pre- 
servation of  manure.  193.  How  does  manure,  produced  in  open 
barnyards,  compare  in  composition  with  that  produced  in  covered 
sheds?  194.  When  may  manure  be  taken  directly  to  the  field  and 
spread?  195.  How  may  coarse  manures  be  injurious  to  crops? 
196.  What  is  gained  by  manuring  pasture  land?  197.  Is  it  econom- 
ical to  make  a  number  of  small  manure  piles  in  a  field  ?  Why  ? 
198.  At  what  rate  per  acre  may  manure  be  used?  199.  To 
what  crops  is  it  not  advisable  to  add  stable  manure?  200.  How 
do  a  crop  and  a  manure  produced  from  that  crop  compare  in 
manurial  value?  201.  Why  do  manures  have  such  a  lasting  effect 
upon  soils?  202.  Why  does  manure  from  different  farms  have 
such  variable  values  and  composition  ?  203.  In  what  seven  ways 
may  stable  manures  be  beneficial  ?  204.  What  may  be  said  regard- 
ing the  importance  of  phosphorus  as  plant  food  ?  What  function 
does  it  take  in  plant  economy  ?  205.  How  much  phosphoric  acid 
is  removed  in  ordinary  farm  crops  ?  206.  To  what  extent 
is  phosphoric  acid  present  in  soils?  207.  What  are  the  sources 
of    the    soil's    phosphoric  acid  ?     208.    What    are  the  commer- 


270  SOILS   AND    FERTILIZERS 

cial  sources  of  phosphate  fertilizers  ?  209.  Give  the  four  cal- 
cium phosphates  and  their  relative  fertilizer  values.  210.  Define 
reverted  phosphoric  acid.  211.  Define  available  phosphoric  acid. 
212.  In  what  forms  do  phosphate  deposits  occur?  213.  State  the 
general  composition  of  phosphate  rock.  214.  Explain  the  process 
by  which  acid  phosphates  are  made.  Give  reactions.  215.  How 
is  the  commercial  value  of  phosphoric  acid  determined?  216. 
What  is  basic  phosphate  .slag  and  what  is  its  value  as  a  fertilizer  ? 
217.  What  is  guano?  218.  How  do  raw  bone  and  steamed  bone 
compare  as  to  field  value  ?  As  to  composition  ?  219.  What  is  dis- 
solved bone?  220.  How  is  bone-black  obtained,  and  what  is  its 
value  as  a  fertilizer?  221.  How  are  phosphate  fertilizers  applied  to 
soils?  In  what  amounts?  222.  How  may  the  phosphoric  acid  of 
the  soil  be  kept  in  available  condition  ?  223.  What  is  the  function 
in  plant  nutrition  of  potassium?  224.  To  what  extent  is  potash 
removed  in  farm  crops  ?  225.  To  what  extent  is  pota.sh  present  in 
soils?  226.  What  are  the  sources  of  the  soil's  potash  ?  227.  What 
are  the  various  sources  of  the  potash  used  for  fertilizers?  228. 
What  are  the  Stassfurt  salts,  and  how  are  they  supposed  to  have 
been  formed?  229.  What  is  kainit  ?  230.  How  nuich  potash  is 
there  in  hard-wood  ashes  ?  231.  In  what  ways  do  ashes  act  on  soils  ? 
232.  How  do  unleached  ashes  differ  from  leached  ashes?  233. 
What  is  meant  b}^  the  alkalimetry  of  an  ash?  234.  Of  what  value, 
as  fertilizer,  are  hard-  and  soft-coal  ashes  ?  235.  What  is  the  fer- 
tilizer value  of  the  ashes  from  tobacco  stems  ?  236.  Cottonseed 
hulls?  237.  Peat-bog  ashes?  238.  Saw-mill  ashes?  239.  Lime- 
kiln ashes?  240.  How  is  the  commercial  value  of  potash  deter- 
mined? 241.  How  are  potash  fertilizers  used?  242.  Why  is  it 
sometimes  necessarv'  to  use  a  lime  fertilizer  in  connection  with  a 
potash  fertilizer?  243.  What  can  be  said  regarding  the  importance 
of  lime  as  a  plant  food  ?  244.  To  what  extent  is  lime  removed  in 
crops?  245.  To  what  extent  do  soils  contain  lime  ?  246,  What  are 
the  lime  fertilizers  ?  247.  Explain  the  phy.sical  action  of  lime  fer- 
tilizers. 248.  Explain  the  action  of  lime  on  heavy  clays.  249.  On 
sandy  soils.  250.  In  what  ways,  chemically,  do  lime  fertilizers 
act?  251.  How  may  lime  aid  in  liberating  potash?  252.  What  is 
marl  ?  253.  How  are  lime  fertilizers  applied  ?  254.  What  is  the 
resiilt  when  land  plaster  is  used  in  excess?  255.  Explain  the 
action  of  salt  on  soils  ?  256.  When  would  it  be  desirable  to  use 
salt  as  a  fertilizer?  257.  Is  soot  of  any  value  as  a  fertilizer?  Ex- 
plain its  action.  258.  Are  sea-weeds  of  any  value  as  fertilizer?  259. 
What  is  a  commercial  fertilizer  ?  An  amendment  ?  260.  To  what 
does  the  commercial  fertilizer  industry  owe  its  origin?  261.  Why 
are  commercial  fertilizers  so  variable  in  composition  ?  262.  Ex- 
plain how  a  commercial  fertilizer  is  made.  263.  Why  are  the 
analysis  and  inspection  of  fertilizers  necessary?     264.  What  are  the 


REVIEW   QUESTIONS  27  I 

usual  forms  of  nitrogen  in  commercial  fertilizers  ?  265.  Of  phos- 
phoric acid  and  potash  ?  266,  How  is  the  value  of  a  commercial  fer- 
tilizer determined  ?  267.  What  is  gained  by  home  mixing  of  fer- 
tilizers ?  268.  What  can  be  said  about  the  importance  of  tillage 
when  fertilizers  are  used?  269.  How  are  commercial  fertilizers 
sometimes  injudiciously  used?  270.  How  may  field  tests  be  con- 
ducted to  determine  a  deficiency  in  available  nitrogen,  phosphoric 
acid,  or  potash?  271.  To  determine  a  deficiency  of  two  elements? 
272.  How  are  the  preliminary  results  verified?  273.  Why  is  it 
essential  that  field  tests  with  fertilizers  be  made  ?  274.  Under  Avhat 
conditions  does  it  pay  to  use  commercial  fertilizers?  275.  What  is 
the  result  when  commercial  fertilizers  are  used  in  excessive 
amounts?  276.  Under  ordinary  conditions,  what  special  help  do 
the  following  crops  require  :  Wheat,  barley,  corn,  potatoes,  man- 
gels, turnips,  clover,  and  timothy?  277.  In  what  ways  do  commer- 
cial fertilizers  and  farm  manures  dififer  ?  278.  Does  the  amount  of 
fertility  removed  by  crops  indicate  the  nature  of  the  fertilizer  re- 
quired? In  what  ways  are  plant  ash  analyses  valuable  ?  279.  Ex- 
plain the  action  of  plants  in  rendering  their  own  food  soluble.  280, 
Why  do  crops  differ  as  to  their  power  of  procuring  food?  281. 
Why  is  wheat  less  liable  to  need  potash  than  nitrogen?  282.  What 
position  should  wheat  occupy  in  a  rotation?  283.  In  what  ways  do 
wheat  and  barley  differ  in  feeding  habits?  284.  What  can  be  said 
regarding  the  food  requirements  of  oats?  285.  Corn  removes  from 
the  soil  twice  as  much  nitrogen  as  a  wheat  crop,  yet  a  wheat  crop 
usually  thrives  after  a  corn  crop.  Why?  286.  What  help  is  corn 
most  liable  to  need  in  the  way  of  food?  287.  What  position  should 
flax  occupy  in  a  rotation?  288.  On  what  soils  does  flax  thrive  best? 
289.  What  is  the  essential  point  to  observe  in  the  manuring  of  po- 
tatoes? 290.  What  kind  of  manuring  do  sugar-beets  require?  291. 
Why  should  the  manuring  of  mangels  be  different  from  that  of  tur- 
nips? 292.  What  may  be  said  regarding  the  food  requirements  of 
buckwheat  and  rape?  293.  What  kind  of  manuring  do  hops  and 
cotton  require?  294.  What  kind  of  manuring  is  most  suitable  for 
leguminous  crops?  295.  What  is  the  object  of  rotating  crops?  296. 
Should  the  whole  farm  undergo  the  same  rotation  system?  297. 
W^hat  is  meant  b}-  soil  exhaustion?  298.  What  are  the  nine  impor- 
tant principles  to  be  observed  in  a  rotation?  299.  Explain  why  it 
is  essential  that  deep  and  shallow  rooted  crops  should  alternate. 
300.  Wliy  is  it  necessary  that  the  humus  be  considered  in  a  rota- 
tion? 301.  What  is  the  object  of  gro\\-ing  crops  of  dissimilar  feeding 
habits?  302.  How  may  crop  residues  be  used  to  the  best  advantage? 
303.  In  what  ways  may  a  decline  of  soil  nitrogen  be  prevented  by 
a  good  rotation  of  crops?  304.  In  what  ways  do  different  crops  and 
their  cultivation  influence  the  mechanical  condition  of  the  soil? 
305.   How  may  the  best  use  be  made  of  the  soil  water?     306.  How 


272  SOILS   AND    FERTILIZERS 

may  a  rotation  make  an  even  distribution  of  farm  labor?  307.  How 
are  manures  used  to  the  best  advantage  in  a  rotation?  308.  In  what 
other  ways  are  rotations  advantageous?  309.  What  may  be  said  re- 
garding long-  and  short-course  rotations?  310.  How  is  the  conser- 
vation of  fertilitv  best  secured?  311.  Why  does  the  use  made  of 
crops  influence  fertility?  312.  W'hat  are  the  essential  points  to  be 
observed  in  the  two  systems  of  farming  compared  in  Section  323? 
313.  Is  it  essential  that  all  elements  removed  in  crops  should  be  re- 
turned to  the  soil  in  exactly  the  amounts  contained  in  the  crops? 
Why?  314.  How  does  manure  influence  the  inert  matter  of  the 
soil?  315.  What  general  systems  of  farming  best  conserve  fertility? 
316.  Under  what  conditions  may  farms  be  gaining  in  reserve  fer- 
tility? 317.  Why  in  continued  grain  culture  does  the  loss  of  nitro- 
gen from  a  soil  exceed  the  amount  removed  in  the  crop? 


CORRECTIONS 

Page  25,  line  19,  for  "three  months,"  read  "two  months." 

Page  28,  line  18,  after  soil,  add  :  "absorbed  from  the  air." 

Page  28,  line  26,  add  :  "when  reduced  below  4  per  cent." 

Page  64,  line  5,  for  "one-half,"  read  "one-tenth." 

Page  72,  line  18,  read"94,"  not  "96." 

Page  150,  line  2,  read  "clover  hay  nitrogen,  35,"  not  "45." 

Page  187,  under  Flax,  transpose  "19"  and  "8." 


INDEX 


Absorbents 143 

Absorption  of  heat  by  soils 42 

Absorptive  power  of  soils 46 

Acids  in  plant  roots 228 

Aerobic  ferments 121,  158 

Agricultural  geology 49 

Agronomy 9 

Albite 56 

Alkaline  soils 87 

Aluminum  of  soils 66 

Amendments 205 

Ammonium  compounds 115 

salts 136 

Anaerobic  ferments 159 

Analysis  of  soil,  how  made-. 73,  74 

of  soil,  value  of 76,  80 

Apatite  rock 58 

Application  of  fertilizer 222 

of  manures 163,  165 

Arrangement  of  soil  particles 16 

Ashes 191 

action  of,  on  soils 192 

testing  of 193 

Assimilation  of  nitrogen 102 

of  phosphates 173 

Atmospheric  nitrogen    104 

Atwater  . .  ■■ 108,  132 

Availability  of  plant  food 79 

Available  phosphates 177,  184 

nitrogen 113,  133 

Barley,  fertilizers  for 223 

food  requirements  of  •  •  •  ■  231 

Blood,  dried 1 28 

Bone,  dissolved 183 

fertilizers 181 

Boneash    182 

Bone-black 183 

Boussingault's  experiments 

4,  104,  105,  106 


Calcium  an  essential  element  ..196 
carbonate  and  nitrific'on  •  123 

compounds  of  soils 67 

phosphate 58,  1 75 

Capillarity   27 

and  cultivation 31 

Carbon  of  soil 63 

sources  for  plant  growth  .  -63 

Chlorine  of  soil 64,  87 

Clay,  formation  of 58 

particles 13 

Clover  as  manure 134 

nitrogen  returned  by 

108,  118,  253 

root  nodules no 

manuring  of- 194,  199,  224,237 

Coal  ashes 193 

Color  of  plants,  influenced   by 

nitrogen 104 

of  soils 45 

Combination  of  elements  in  soils- 61 

Commercial  fertilizers 205,  225 

and  tillage 216 

abuse  of 216 

extent  of  use 205 

field  tests  with 218 

home  mixing  of 214 

inspection  of 209 

mechanical  condition  of  -210 

nitrogen  of 210 

phosphoric  acid  of 211 

potash  of 212 

proper  use  of 217 

valuation  of 213 

Composition  of  soils 83,  85 

Composting  manures 160 

Corn ,  fertilizers  for 223 

food  requirements  of  -  ■  -  •  232 

and  manure   167 

Cotton,  fertilizers  for 235 


274 


INDEX 


Cottonseed  meal 132 

Cow  manure 152 

Crop  residue 239 

Cultivation  after  rains 33 

shallow  surface 31 

Davy,  work   of 3 

Dissolved  bone 1 83 

Distribution  of  soils 54 

Denitrification 123 

De  Saussure,  work  of 3,  104 

Drainage 41,  43 

Dried  blood   128 

Dyer 80 

Early  truck  soils 19 

Electricity  of  soil 47 

Evaporation 30 

Excessive  use  of  fertilizers 222 

Experiments 259 

Fallow  fields 126 

Fall  plowing 35 

Farm  manures 141,  171 

Farm  manures  and  commercial 

fertilizers 224 

Feldspar 55,  209 

Fermentation  of  manures 158 

Fertility,  conservation  of 249 

removed  in  crops 227 

Fertilizers,  amount  to  use 222 

influence  upon  soil  water. 39 

on  barley 231 

on  wheat 230 

Field  tests  wath  fertilizers 218 

Fine  earth 12 

Fish  fertilizer 132 

Fixation 1 38 

Flax,  food  requirements  of 233 

soils  20 

Flesh  meal 131 

Forest  fires 97 

Formation  of  soils 49,  54 

Form  of  soil  particles 14 

Fruit  soils 20 


Gains. of  humus 100 

of  nitrogen 117 

Glaciers,  action  of 51 

Grain  soils 22 

Granite 58 

Grass  lands,  fertilizers  for 236 

Grass  soils 22 

Guano  181 

Gypsum  and  manure 161 

Heat  and  crop  growth 44 

produced  by  manures 160 

of  soil 42,  43 

Heiden 156,  161 

Hellriegel   25,  30,  109 

Hen  manure 154 

Hog  manure 154 

Hops,  fertilizers  for 236 

Horse  manure 152 

Human  excrements 156 

Humates 91 

as  plant  food 95 

Humification 92 

Humic  acid 98 

Humic  phosphates 92,  184 

Humus 91 

active  and  inactive 100 

causes  fixation 139 

composition  of 94 

Income  and  outgo  of  fertility.. 

250,  253 

Injury  of  coarse  manures   ••40,  164 

Insoluble  matters  of  soils 70,  71 

Iron  compounds  of  soil 68 

Kainit 190,  206,  212 

Kaolin 58 

King 32,  35,  36 

Lawesand  Gilbert.. 7,  107,  229.  230 

Leached  ashes 192 

Leaching  of  manure 157 

Leather 133 

Leguminous  crops,fertilizers  for,  237 
as  manure 134 


INDEX 


275 


Liebig 6,  7,  156,  227 

Liquid  manure 147 

Lime,  action  on  soils 198 

amount  of,  in  soils 197 

amount  removed  in  crops  •  1 97 

excessive  use  of 201 

fertilizers 196 

indirect  action  of 199 

physical  action  of 201 

use  of 20  r 

and  acid  soil 198 

and  clover 1 99 

Loam  soils 24 

Loss  of  fertility  in  grain  farming, 252 

Loss  of  humus 97 

of  nitrogen 117,  126 

Losses  from  manures 157,  158 


Magnesium  compounds  of  soils  • .  68 

salts  as  fertilizers 202 

Mangels,  fertilizers  for 224 

Manure  from  cow 152 

hen 154 

hog 154 

horse 152 

sheep 153 

Manures,  farm 141 

influenced  by  foods 144 

use  of,  in  rotations 243 

value  of J  70 

and  soil  water 39,  98 

Manurial  value  of  foods 149 

Manuring  of  crops 166 

pasture  land 164 

Marl 200 

Mechanical  analysis  of  soils 17 

condition  of  fertilizers.  •  -210 
Methods  of   farming,  influence 

of,  upon  fertility 100 

Mica 57 

Micro-organisms   and   soil    for- 
mation   49.  53 

Mixing  manures 155 

Movement  of  water  after  rains.. 33 
Mulching  36 


Nitrate  of  soda 135 

Nitric  nitrogen 136 

Nitrification 119 

conditions  necessary  for  120 

and  sunlight 122 

and  plowing 127 

Nitrogen  assimilation 104 

as  plant  food 102 

compounds  of  soil 65 

deficiency  of,  in  soil 219 

losses  of,  from  soil 117 

ratio  of,  to  carbon 116 

removed  in  crops 114 

of  commercial  fertilizers. 210 

amount  of,  in  soils 113 

as  organic  forms 112 

as  nitrates 114 

availability  of 113 

forms  of 112 

origin  of 1 1 1 

Nitrogenous  manures 128 

Number  of  soil  particles 17 

Odor  of  soils 46 

Organic  acids,   action   of,   upon 

soils 79,  80 

Organic     compounds     of     soil, 

classification  of 90 

source  of 90 

Organic  nitrogen 128,  133 

Organisms,  ammonia-producing,  1 23 

of  soil 124 

nitrifying 1 20 

products  of 125 

Osborne 1 8 

Orthoclase 56 

Oxidation  in  soil 43 

Peat 134,  144 

Percolation 28 

Permeability  of  soils 38 

Phosphate  fertilizers 172 

use  of 183 

rock 177 

slaar 180 


276 


INDEX 


Phosphoric  acid  of  commercial 

fertilizers 211 

acid  in  soils 174 

acid,  deficiency  of 220 

acid  removed  in  crops 173 

Phosphorns  compounds  of  soils.  .64 

Physical  property  of  soils 10,  47 

modified  by  farming lor 

Plant  food,  classes  of 69,  70 

ash  and  fertilizers 226 

Plowing,  depth  of 37 

fall   35 

spring 36 

influences  nitrification.  . .  127 

Potash  fertilizers 186 

fertilizers,  use  of  • .  •  •  ....  194 
of  commercial  fertilizers .  2 1 2 

in  soils 188 

in  soils,  sources  of 188 

removed  in  crops 187 

and  lime,  joint  use  of 194 

Potassium  compounds  of  soil ...   67 

Potato,  fertilizers  for 224 

food  requirements  of 233 

soils  19 

Questions 265 

Rainfall  and  crop  production ...  25 

Rape,  food  requirements  of 235 

References 255,  257 

Reverted  phosphoric  acid 176 

Roberts 37,  157 

Rocks,  composition  of 55,  59 

Rock  disintegration 49 

Rolling 34 

Roots,  action  on  soil 228 

Rotation  of  crops 238,  254 

of     crops,   principles  in- 
volved   239 

length  of 244 

problems 248 

and  farm  labor 243 

and  humus 241 

and  insects 244 

and  soil  nitrogen 241 


Rotation  and  soil  water 242 

and  weeds 244 

Salt  as  a  fertilizer 202 

Sand,  grades  of 13.  H 

Seaweeds  as  fertilizers   203 

Sedentar}'  soils 54 

Seed  residues 132 

Sheep  manure 153 

Silicon  and  silicates 163 

Silt  particles 14 

Size  of  soil  particles 12 

Skeleton  of  soils 12 

Small  manure  piles 165 

Sodium  compounds  of  soil 68 

Soil,  composition  of 83,  85 

exhaustion  238 

types 19 

Soot  203 

Specific  gravity  of  soil 12 

Spring  plowdng 36 

Stockbridge 12,  25 

Stock  farming  and  fertility 254 

Storer 63,  1 29 

Stutzer 133 

Sub-soiling 35 

Sugar  beets,  fertilizers  for 234 

beet  soils 21 

beets  and  farm  manures.  .167 

Sulphate  of  potash 190 

Sulphur  compounds  of  soil   64 

Superphosphates    178 

Tankage  130 

Taste  of  soils 46 

Temperature  of  soils 42 

Tests  with  fertilizers 218 

Thaer,  work  of 3 

Tobacco,  manuring  of 167 

Tobacco  stems 193 

Transported  soils 54 

Truck  farming  and  fertilizers  ..221 
Turnips,  fertilizers  for 224 

Ville 107 

Volcanic  soils 55 


INDEX 


277 


Volume  of  soils 12 

Voorhees 214 

Water,  action  of,  upon  rocks  and 

soils   50 

bottom 26 

capillary   27 

capillary,  conservation  of 

31,  32,  33 

hydroscopic 28 

losses  by  evaporation 30 

losses  by  transpiration 30 

of  soil 26,  41 

of  soil  influenced — 

by  drainage 41 

plowing.. 35,  36 
forest  regions,  4 1 
manures.  .39,  98 


Water  of  soil  influenced — 

by  mulching.  •  •  .36 

rolling  ... 34 

subsoiling  •  •  -35 

required  by  crops 25 

W^arington 119,121,  123,  229 

Weeds,  fertility  in 203 

Weight  of  soils 11 

Wheat,  fertilizers  for 223 

food  requirements  of  - .  • .  229 

soils 22,  23 

Whitney 17,  47 

Wilfarth 109 

Wood  ashes 191 

Wool  waste 204 

Zeolites 57,  139 


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